The authors evaluated the risk of development of cholelithiasis in 6050 patients treated at a single hospital for various childhood cancers with different therapeutic modalities, including chemotherapy, surgery, radiation therapy, and bone marrow transplantation, from 1963 to 1989. Patients with underlying chronic hemolytic anemia or preexisting gallstones were excluded. Nine female and seven male patients with a median age of 12.4 years (range, 1.2 to 22.8 years) at diagnosis of primary cancer had gallstones develop 3 months to 17.3 years (median, 3.1 years) after therapy was initiated. Cumulative risks of 0.42% at 10 years and 1.03% at 18 years after diagnosis substantially exceed those reported for the general population of this age group. Treatment-related factors significantly associated with an increased risk of cholelithiasis were ileal conduit, parenteral nutrition, abdominal surgery, and abdominal radiation therapy (relative risks and 95% confidence intervals = 61.6 [27.9-135.9], 23.0 [9.8-54.1], 15.1 [7.1-32.2], and 7.4 [3.2-17.0], respectively). There was no correlation with the type of cancer, nor was the frequency of conventional predisposing features (e.g., family history, obesity, use of oral contraceptives, and pregnancy) any higher among the affected patients in this study than in the general population. Patients with cancer who have risk factors identified here should be monitored for the development of gallstones.