Over the past two decades, the use of antidepressant medications has grown to the point that they are now the third most commonly prescribed class of medications in the United States. Much of this growth has been driven by a substantial increase in antidepressant prescriptions by nonpsychiatrist providers without an accompanying psychiatric diagnosis. Our analysis found that between 1996 and 2007, the proportion of visits at which antidepressants were prescribed but no psychiatric diagnoses were noted increased from 59.5 percent to 72.7 percent. These results do not clearly indicate a rise in inappropriate antidepressant use, but they highlight the need to gain a deeper understanding of the factors driving this national trend and to develop effective policy responses. To the extent that antidepressants are being prescribed for uses not supported by clinical evidence, there may be a need to improve providers' prescribing practices, revamp drug formularies, or vigorously pursue implementation of broad reforms of the health care system that will increase communication between primary care providers and mental health specialists.