The prevalence of sludge and stones in the gallbladder of 298 women in the immediate post-partum period was ultrasonographically assessed. We have investigated some risk factors for the development of sludge or stones in these patients and followed up most of these patients by ultrasonography to detect the presence of sludge and/or stones in the year following their discovery. We found sludge in 80 (26.2%) and gallstones in 16 (5.2%) of these patients. Age, obesity and months of oral contraceptive use were risk factors only for the presence of gallstones. After 1 year of follow-up only 2 out of 45 patients with sludge but 13 out of 15 patients with gallstones still had abnormal ultrasonographic findings.