This study aimed to provide preliminary data on the tolerability and effectiveness of citalopram for patients with dysthymic disorder. Twenty-one adult subjects meeting DSM-IV criteria for dysthymic disorder were enrolled in this 12-week open-label study, of whom 15 had pure dysthymia (e.g. no major depression in the past 2 years). Citalopram was initiated at 20 mg/day, and increased to a maximum of 60 mg/day. Response was defined as 50% or greater drop in score on the Hamilton Depression Rating Scale (HDRS) and a Clinical Global Impressions-I score of 1 ('very much improved') or 2 ('much improved'). Of these 15 pure dysthymic disorder subjects, all completed the trial, and 11 (73.3%) were treatment responders. All paired sample t-tests were highly significant, demonstrating significant average improvement on all measures of symptomatology and functioning. Scores on the 24-item HDRS decreased from 22.3+/-4.3 at baseline to 9.1+/-7.8 at week 12 [t(14)=6.1, P<0.001]. In addition, improvement was noted in self-reported measures of temperament and social functioning. The average final dose of citalopram was 39 mg/day. Side-effects were reported by nine of 15 subjects (60%), most frequently gastrointestinal symptoms (n=5), dry mouth (n=5) and sexual side-effects (n=3). These findings suggest the effectiveness and tolerability of citalopram in treating dysthymic disorder. Double-blind prospective studies are needed comparing citalopram both to placebo and to other medications, assessing both initial and sustained response to treatment.