This prospective study demonstrated that among 92 consecutive patients who underwent cholecystectomy for gallstones at an urban university hospital, 27% had pigment stones and 73% had cholesterol stones. Age, sex, and weight, but not race, were significant determinants of stone type. The mean hemoglobin, direct and total serum bilirubin, and fasting glucose concentrations were similar for each group. The presence of alcoholism, diabetes, thyroid disease, or heterozygous hemoglobinopathy did not influence stone type. The average patient with pigment stones is a lean man or woman 63 years old; in contrast the composite patient with cholesterol stones is a modestly overweight woman 43 years old.