We report two cases of psoas abscess complicating Crohn's disease. A 24-year-old woman and an 18-year -old man, who had been on medication for Crohn's disease, began to experience right lower abdominal pain, mild lower back pain, and fever. In both cases, CT scanning demonstrated a low-density area within the right iliopsoas muscle, which suggested abscess formation. Both patients underwent drainage of the abscess with resection of the diseased bowel. Postoperative courses were uneventful. Crohn's disease has been known as one of the most common etiologies of psoas abscess in Western countries, but this complication was thought to be uncommon in Japan. The difference is due to the low incidence of the Crohn's disease, which is from a tenth to a fifth of that in Western countries. However, with an increase in the number of patients of Crohn's disease, reports on this complication have been appeared. In some cases without typical signs such as limb pain and hip contracture, it is difficult to diagnose psoas abscess. Because failure to recognize and treat psoas abscess results in considerable morbidity, physicians should be alert to the possibility of a psoas abscess if a segment of the diseased bowel is adherent to the anterior psoas fascia. Curettage and drainage of the abscess with resection of the diseased segment of the bowel is recommended, because of the risk of recurrence after medical therapy.