Post-stroke pathological crying is a distressing condition in which episodes occur in response to minor stimuli without associated mood changes. There is preliminary evidence of disturbed serotoninergic neurotransmission in such cases. We investigated the effect of the selective serotonin reuptake inhibitor citalopram on uncontrolled crying in stroke patients in a double-blind placebo-controlled crossover study. 16 consecutive patients (median age 58.5 years, range 40-83) entered the 9-week study a median of 168 days (range 6-913) post stroke and were treated with citalopram 10-20 mg daily for 3 weeks. Crying history was determined from semistructured interviews and from diaries kept by the patients. Psychiatric assessment was made with the Hamilton depression scale (HDS), and unwanted effects were measured with the UKU side-effect scale. In 13 patients in whom frequency of crying could be assessed, the number of daily crying episodes decreased by at least 50% in all cases during citalopram treatment vs 2 patients during placebo treatment (p < 0.005, McNemar's test), the effect being rapid (1-3 days) and pronounced in 11 (73%). There was a concomitant significant decrease in depression rating from HDS 8.9 to 5.3 (p < 0.005, Wilcoxon's test). Citalopram was well tolerated, the few side-effects being mild and transient. We conclude that serotoninergic neurotransmission plays an important part in post-stroke pathological crying and that citalopram is an effective and well-tolerated treatment.