We tracked changes in use of mental health care services and self-reported unmet need from 2001 to 2005 using the California Health Interview Survey, a repeated cross-sectional survey. A total of 56,270 and 43,020 adults aged 18 years or older were included in waves 2001 and 2005, respectively. Perceived need for mental health care was assessed with the question, "During the past 12 months, did you think you needed help for emotional or mental health problems, such as feeling sad, blue, anxious, or nervous?" Among those expressing need, use of mental health care services was assessed with the question, "Not counting overnight stays, emergency room visits, or visits for drug or alcohol problems, in the past 12 months, have you seen a psychiatrist, psychologist, social worker, or counselor for emotional or mental health problems?" We defined unmet need as expressing need but not having used services.