OBJECTIVE: This study was designed to assess the ulnar nerve using ultrasonographic measures at the elbow in patients with cubital tunnel syndrome. METHOD: We examined 20 healthy men as control and 10 patients with cubital tunnel syndrome. We measured the short, long axis and area of ulnar nerve with the shoulder abducted at 60o and elbow fully extended posture in prone position. The mean age of control and patients were 46.4 (30-60) years old and 48.8 (30-61) years old, respectively. RESULTS: In normal group, the size of ulnar nerve at medial epicondyle, 5 cm proximal to medial epicondyle and 5 cm distal to medial epicondyle was 4.0x2.0 mm, 6.2 mm2, 3.7x 2.1 mm, 5.8 mm2 and 3.7x2.0 mm, 6.0 mm2 respectively, where as in the patients group, it was 5.7x2.9 mm, 13.1 mm2, 5.2x3.1 mm, 12.7 mm2 and 4.7x2.8 mm, 10.2 mm2 respectively. In cubital tunnel syndrome, the size of ulnar nerve was smaller in the distal portion of the medial epicondyle compared to the size measured at proximal or medial epicondyle. There was significant differences between the size of the ulnar nerve in controls and patients with cubital tunnel syndrome (p<0.05). CONCLUSION: The ultrasonography can accurately detect the morphologic changes in the ulnar nerve, so it will be useful in diagnosis of cubital tunnel syndrome.