Psoas abscess were found in 6 cases among 166 patients with Crohn's disease between 1985 and 1989; in one case, it was the first sign of Crohn's disease. Diagnosis was usually difficult and should be suspected on the following signs: lower abdominal quadrant pain, psoitis, abdominal mass, sciatica or pain along the course of the femoral nerve. Diagnosis was confirmed in nearly all cases by computerized axial tomography. Effective therapy combines drainage and bowel resection.