Severe acute respiratory syndrome (SARS) is an emerging infectious disease and diarrhea has been reported in up to 76% of cases. The purpose of the present paper was to carry out a retrospective study of the clinical and demographic data of SARS patients with diarrhea in Princess Margaret Hospital. From 1 to 31 March 2003, hospital records from 240 patients with confirmed SARS were studied. Patients with watery stool of >/=3 times/day for at least 3 consecutive days were defined as the diarrhea group. Clinical and demographic data were compared between the diarrhea and non-diarrhea groups. Chest X-ray (CXR) scores during the peak of diarrhea period were recorded by a respiratory physician. These CXR scores were correlated with the peak frequency of diarrhea by Spearman's correlation coefficient. Diarrhea occurred in 20.4% of patients after admission. Female patients were predominant with a female to male ratio of 6:1 (P < 0.001) and 69.4% of patients were living in Amoy Gardens Estate (P = 0.01). The proportions of patients requiring ventilatory care and mortality in the diarrhea group were 8.2% and 2%, respectively, which were significantly lower than those in the non-diarrhea group (27.6% and 16.2%, P < 0.005). The CXR scores during the peak of diarrhea were not correlated with the maximum frequency of diarrhea (r = -0.09, P = 0.5). A total of 20.4% of SARS patients had the complication of diarrhea after hospital admission. Both female sex and being a resident of Amoy Gardens Estate were associated with diarrhea. The diarrhea group had a better prognosis.