The author describes a day treatment program using responsibility therapy, a form of behaviorism based on the principles of Alcoholics Anonymous. Mental illness is conceptualized as an addiction or bad habit to be corrected through definition of the client's problems, values, and therapeutic objectives. The program, which is operated by the county, requires high client motivation and the involvement of significant others. About 100 clients enter the program each year; more than half are referrals from the county probation department. A recent study showed that the program is serving the most disabled group of clients at least as effectively as the other county services.