What Does NOS Mean?

When you look at your medical records, medical bills or other formal paperwork from a doctor’s office, you might see the abbreviation “NOS” somewhere. This might seem frightening, but it has a very simple explanation. Here’s what “NOS” means in the medical context, and what that might mean for you. Besides as a medical abbreviation, NOS has other meanings such as new old stock in retail and auction industry.

What does NOS Mean as a Medical Abbreviation?

“NOS” simply means “Not Otherwise Specified.” It’s an abbreviation that helps doctors choose from a standard list of codes that tell the diagnosis of your medical condition. In most cases, a standard list has very specific codes that cover just about everything. But your condition might be something that isn’t specified in that list, and so your doctor chooses “NOS” instead.

For instance, you might have an anxiety disorder. There are many particular kinds of anxiety disorders, but what if yours doesn’t fall within any of those pre-set codes? Your doctor would choose “Anxiety NOS” which means “anxiety disorder, not otherwise specified.”

Another example might be knee pain. If you suffer from knee pain, you might go to the emergency room, and then be sent to have x-rays or other work done. They can’t find the cause, and tell you to follow up with your doctor. In the meantime, they have to enter a code for your insurance company. Since they can’t specify what caused the knee pain, they might use the term “Arthralgia NOS,” which means “joint pain, not otherwise specified.”

Examples of NOS as Medical Conditions


PDD-NOS is one of the three autism spectrum disorders. This one in particular is “pervasive developmental disorder not otherwise specified,” which is also known as atypical autism. This is because the symptoms don’t quite fit the other medical codes or descriptions for the condition.


“Personality disorder not otherwise specified” pertains to those who have issues with personality disorders, but nothing that fits neatly into any designated code. Other personality disorders specified are sadistic personality disorder, depressive personality disorder, passive–aggressive personality disorder and self-defeating personality disorder.


“Mood disorder not otherwise specified” means that there is something wrong, but the diagnosis codes given don’t do justice to the problem. Thus the MD-NOS is filed. Keep in mind this is not a diagnosis, but rather just a way of filing a code that suits an approximate diagnosis.


Common eating disorders include anorexia, bulimia, and others that have become a part of mainstream lexicon. But there are several eating disorders that don’t fit neatly into those categories, and so there is “eating disorder not otherwise specified.”


This designation means “depressive disorder not otherwise specified,” which means that someone has a form of depression that is impairing their day-to-day life, but it doesn’t fit into any of the regular codes for insurance or diagnostic purposes.

What Are Other Meanings of NOS?

Though medical uses are some of the most common reasons you might see NOS, there are other uses for the phrase as well. These phrases might be very commonly used, or they might be obscure. We have included several of them here; however, keep in mind that this is not an exhaustive list. There could be other uses of “NOS” abbreviation that are not included here.

1. New Old Stock

A very commonly used phrase in the retail and auction business, this stands for items being offered for sale that were manufactured a very long time ago, and thus aren’t really ‘new.’ This can refer to obsolete equipment, or parts for that obsolete equipment. That old stock might represent all that is available of that particular item, even though it was manufactured many years ago.

A good example of this is an old typewriter that requires a ribbon and ink, as well as strips of correction paper. These items might not be produced on a broad scale any longer, but there could be “old stock” that was produced many years ago that is still for sale. As you might imagine, this term is a very common one for those who are interested in antiques, classic cars and the like.

2. National Occupational Standards

This stands for standards of performance that are used in the United Kingdom. These are lists of expectations for work, including the knowledge and skills a person needs in order to perform a job to the best of their ability.

3. In Information technology

In the world of information technology, acronyms and abbreviations are very common. “NOS” is used more than once in this field, and might mean “network operating system.” It might also mean “Nokia OS,” which is an operating system for Nokia cell phones, or a type of software called “NOS,” which is an operating system for the Control Data Corporation Cyber, a line of mainframe computers.

4. In Science

The abbreviation “NOS” also has a place in the world of science. Many people might recognize it has a shortened form of “Nitrous Oxide,” which is often used in racing engines. It is also referred to as “nitrous” and has been used often in pop culture film that involves racing cars. It also stands for the lesser-known “nitric oxide synthase,” which is a class of enzymes. “NOS” can also be used as an acronym, such as for the “National Ocean Service” (part of the National Oceanic and Atmospheric Administration) and the “National Ornithological Society,” which is a society for bird-watchers.

In other words, the term “NOS” can be found almost anywhere. But if you find it in your medical files, you might be concerned. It is important to remember that “not otherwise specified” in a diagnosis or billing code is nothing to worry about, and simply means that the medical literature or billing codes don’t include your specific condition, or that your doctor hasn’t figured out exactly what is going on yet. Either way, “NOS” is no reason for worry.

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