Personality disorders are generally thought not to change by much over time. We assessed the personality status of 202 patients who had a defined diagnostic and statistical manual (DSM)-III neurotic disorder, dysthymia, panic disorder, or generalised anxiety. All patients had had drug and psychological treatment in a randomised controlled trial. 12 years after entry to the study, we reassessed the personality status of 178 (88%) of these patients using the same test (personality assessment schedule). The personality traits of patients in the cluster B flamboyant group (antisocial, histrionic) became significantly less pronounced over 12 years, but those in the cluster A odd, eccentric group (schizoid, schizotypal, paranoid), and the cluster C anxious, fearful group (obsessional, avoidant) became more pronounced. The measure of agreement between baseline and 12-year personality clusters was poor or slight (kappa=0.14, 95% CI 0.04-0.23). Our results suggest that the assumption that personality characteristics do not change with time is incorrect.