Although toxicity due to acute and chronic use of bismuth salts is well known, nephrotoxicity after ingestion of colloidal bismuth has been reported in few cases so far. Here we report the first case of acute renal failure (ARF) due to colloidal bismuth subcitrate overdosage in childhood. A 2-year-old boy was admitted to the hospital 6 h after ingestion of 28 De-Nol tablets (colloidal bismuth subcitrate 8.4 g). On admission, physical examination was unremarkable and he showed no signs of encephalopathy. Initially gastric lavage was performed then appropriate fluid therapy was started. ARF associated with uremia and oliguria developed on day 2 and peritoneal dialysis therapy was prescribed on day 4 for 10 days. Blood and urine bismuth levels were 739 micrograms/l and 693 micrograms/l, respectively, 10 days after the pills had been taken. His urine volume gradually increased and plasma BUN and creatinine levels decreased during peritoneal dialysis. On day 20 post-admission, plasma BUN and creatinine were 14 mg/dl and 0.7 mg/dl, respectively. Blood bismuth levels were 96 micrograms/l on day 60 and 12 micrograms/l on day 105. Now the patient is well and has no problem. This case suggests that ARF may develop in children following colloidal bismuth subcitrate overdosage; the prognosis is good, and peritoneal dialysis may be useful in these cases.