During the 5 years 1985-1989, 24 (32%) of 76 patients treated for Hirschsprung's disease (HD) developed enterocolitis, this being present at the time of diagnosis in 10 (13%) infants, 7 of whom were neonates. HD presented as necrotizing enterocolitis in 5 neonates, 4 of whom were premature. The enterocolitis developed postoperatively in 14 (18%) patients, in 7 after an enterostomy and in 7 after a pull-through procedure. Recurrent episodes of enterocolitis occurred in 4 of the patients who developed postoperative enterocolitis. The risk of enterocolitis was increased in girls, in patients with associated Down's syndrome, those with a family history of HD, and those managed by an endorectal pull-through procedure. The Duhamel procedure was associated with a low (5%) incidence of postoperative enterocolitis. Long-segment aganglionosis was not associated with an increased risk of enterocolitis and preoperative enterocolitis conferred no increased risk of postoperative enterocolitis.