We report a rare complication of of ritual circumcision in an 8-week-old boy. He presented 1 week after the procedure with reduced urine output, a grossly distended bladder and marked bilateral hydroureteronephrosis on ultrasonography. The acute partial urinary obstruction was due to the dressing which was applied after surgical removal of the foreskin and to oedema of the glans. He had abnormal renal function (creatinine 85 μmol/l, urea 8.5 mmol/l) and a hyperkalaemic metabolic acidosis with hyponatraemia (Na 127 mmol/l, K 6.9 mmol/l, HCO3 16 mmol/l), which were attributed to obstructive uropathy. Because of prolonged secondary bladder dysfunction he required urinary catheterisation for 1 week. There was significant post obstructive diuresis and parenteral fluid therapy was given for 7 days. Whilst urinary retention is a well recognised complication of circumcision, this is the first report of significant obstructive uropathy and renal impairment due to surgical excision of the foreskin.