Ten of a total of 106 children with chronic inflammatory bowel disease seen between 1973 and 1983 were aged 3 years or less (9%). These are the subject of this study. Colonoscopy and biopsy revealed ulcerative colitis in two, Crohn's disease in two, cow's milk-induced colitis in two, and colitis of indeterminate type in four. The children were followed up and reassessed 2 years post-treatment. The four children with ulcerative colitis and Crohn's disease were asymptomatic 6 months after treatment with sulfasalazine and/or prednisolone. The two breast-fed infants with allergic colitis who were treated with cow's milk-free diet in baby and mother showed clinical, endoscopic, and histological resolution. One of the remaining four children with indeterminate colitis is well and off all treatment, and two are well with minimal symptoms and taking sulfasalazine. One child continued to have frequent relapses and subsequently had subtotal colectomy performed with clinical improvement. Histopathology showed features suggestive of intestinal Behcet's disease. The present study shows that colonoscopy and mucosal biopsy allow a firm diagnosis to be established in 60% of cases of this selected group of very young children. In our experience colitis in infancy and early childhood appears to be a heterogeneous group of conditions. An initial assessment of indeterminate colitis should be followed with multiple mucosal biopsies to attempt further categorization.