Two personality questionnaires, the MMPI and 16PF, were administered routinely to drug abusers admitted to a newly established hierarchical type of therapeutic community. Questionnaires were repeated at 6 and 12 months with those residents who remained. Comparison of the results with other studies suggests that drug abusers admitted to different treatment centres display a recognizable pattern of personality disturbance, characterized by a combination of neurotic, psychopathic and psychotic elements and an unusual degree of willingness to admit to socially undesirable traits. Twenty-five per cent of residents stayed longer than 6 months. They showed a significant reduction in measured personality disturbance, and at 1 year anxiety was the only outstanding indication of disturbance. The relationship between these results, possible sources of bias and other indices of behaviour change is discussed.