A total of 105 psychiatric inpatients (55 men, 50 women) were investigated for gallstones and associated factors by means of ultrasonography. Gallstones were detected in 27 (26%) of the 105 patients. The overall incidence tended to be higher in female patients than in males. The duration of mental illness and neuroleptic medication in patients with gallstones was significantly longer than in those without gallstones. A stepwise discriminant analysis revealed that the duration of neuroleptic medication was the most informative for discrimination between the 2 groups. These results, in combination with previous studies on the effects of neuroleptics on the bile and biliary system, suggests that neuroleptics may accelerate the formation of gallstones.