For a long time, insurance companies set a limit on the number of therapy sessions their members could receive each year, and refused to pay for additional sessions, regardless of the client's condition or need. Typically, the maximum was 24 sessions or less a year. That adds up to less than every other week - certainly less than the weekly sessions most therapists and clients prefer.
Insurance policies still specify these session limits, but thankfully, many clients are now exempt, thanks to legislation requiring "parity." Basically, the law now requires that mental health problems with a "biological" basis receive coverage equal to that provided for (physical) medical conditions. In other words, if the insurance company would not put a session limit on the number of times you could see a physician for diabetes, it cannot then limit the number of times you see your therapist for Bipolar Disorder.
This is good news for therapists - we can now see clients as frequently as they need to be seen, rather than disrupting the momentum of treatment with inconsistent session, and/or breaking off treatment when it is still needed...if they have a problem classified as "biologically based."
That, of course, raises all kinds of new issues. For example, while it is usually relatively clear that a medical condition has a biological basis, it can be harder to determine which mental or emotional conditions have a biological cause or component. Postmodern, constructionist theories suggest that diagnosis and etiology are to a large extent an extension of socially agreement rather than objective "fact." Thus, our diagnostic categories may be more about what DSM committees agree upon than about clear biological distinctions.
When we make decisions about which diagnosis to assign and/or bill for, there's often more than one that may be appropriate. Since NOT all diagnosis are covered by parity, it behooves us and our clients to familiarize ourselves with the federal and state parity laws. For example, Major Depressive Disorder is classified as a biologically-based condition, but Dysthymic Disorder and Depressive Disorder NOS are not. Diagnositc decisions therefore carry a lot of weight. Similarly, when it comes to billing, if someone has multiple diagnoses, but only one is classified as "biologically based," you would want to list that one as the primary billing diagnosis (since if you list the other, your claims will be denied after the session limit has been reached).
Overall, parity is a good thing: it allows clients to receive needed services much more consistently than before the law was passed. However, it does raise important questions about the nature of mental and emotion issues, the nature of (mental) healthcare, and the way we define diagnosis and etiology. We have many more questions to answer before we call really say that we have achieved "parity."