Avascular necrosis (osteonecrosis) occurs in Crohn's disease, but the rate of this particular complication is not known. Over 20 years, 877 patients with Crohn's disease, 492 women (56.1%) and 385 men (43.9%), were evaluated with patient follow-up data available for a mean of 7.8 years. In this group, four men were seen with osteonecrosis. No woman was affected. All patients had typical radiological, magnetic resonance imaging or pathological changes of osteonecrosis involving the femoral heads, while two also had superimposed avascular necrosis involving the humeral heads. Patient ages ranged from 19 to 36 years at the time of diagnosis of their Crohn's disease, and all were white. In one patient, disease was confined to the colon, while three patients had disease involving the terminal ileum and colon. Disease behaviour in two patients was classified as penetrating because of concomitant ischiorectal abscesses, while one patient developed a metastatic colon carcinoma. Ankylosing spondylitis was present in two patients, but no other extraintestinal manifestations developed. Two patients received corticosteroids as well as parenteral nutrition during the course of their disease. Two patients did not receive corticosteroids or parenteral nutrition. Of 877 patients with Crohn's disease, 484 (55. 1%) received corticosteroids during the course of the disease, 196 (22.4%) received at least one course of parenteral nutrition, and 125 (14.3%) received both corticosteroids and parenteral nutrition. A total of 311 patients (35.5%) had at least one small intestinal resection. The overall rate of avascular necrosis in Crohn's disease was less than 0.5% but for men with Crohn's disease was about 1%. In this series, risk of osteonecrosis could not be attributed to corticosteroid use, parenteral nutrition or both forms of therapy administered together. Small intestinal resection with loss of small intestinal absorptive area was not a risk factor for the development of osteonecrosis. Avascular necrosis (or osteonecrosis) is a very rare extraintestinal osseous complication that may occur in Crohn's disease, independent of previously reported risk factors, including corticosteroids or parenteral nutrition with lipid emulsions.