I have a friend who has always lied -- big rotten lies and stupid little lies. I have also met other people who are just like my friend, constantly lying. Is there a name for this pattern? How is it helped? My friend has made up very damaging lies about all kinds of terrible things, like cheating on spouses and rape. Her lies are often about family members and often involve sex. Then she'll lie about something really stupid and insignificant, like it doesn't matter anyway. -- A Friend

There are several possible reasons -- or labels -- for your friend's behavior. People who lie constantly are often called pathological liars. That's not an official clinical diagnosis, which means it's not listed in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, or DSM-IV. But chronic lying in adults is often a manifestation of antisocial personality disorder (also known as sociopathy). Sociopaths are often deceitful and manipulative in order to gain personal profit or pleasure.

Sometimes an individual with dissociative identity disorder (DID), formerly known as multiple personality disorder, will deny doing things for which they have amnesia (don't remember). In such situations, the person may have no memory of doing X and swear up and down that it didn't happen. But anyone who actually saw the DID individual engaging in the disputed behavior will believe he or she is just lying. Obviously, the situation is more complicated than that. (Of course, some people with DID can also have sociopathic tendencies and intentionally lie about some things.)

Sometimes an individual with dissociative identity disorder (DID), formerly known as multiple personality disorder, will deny doing things for which they have amnesia (don't remember). In such situations, the person may have no memory of doing X and swear up and down that it didn't happen. But anyone who actually saw the DID individual engaging in the disputed behavior will believe he or she is just lying. Obviously, the situation is more complicated than that. (Of course, some people with DID can also have sociopathic tendencies and intentionally lie about some things.)

DID is treatable with long-term psychotherapy. So is antisocial personality disorder, although such individuals will often not seek out treatment on their own or not follow through on treatment once it begins. (The earlier the treatment occurs, though, the better the chances of success.) Sometimes adults with antisocial personality disorder will be motivated for treatment when consequences of their behavior -- such as legal or financial trouble -- cause them distress.

Of course, only your friend really knows the reason for her chronic lying, and ultimately it's up to her to get the help she needs. Until then, you'd probably do yourself (and perhaps her) a favor by refusing to take whatever she says at face value ... at least not until she demonstrates that her word can be trusted.