The clinical profile of thromboangiitis obliterans (TAO) has been changing. The purpose of this study was to clarify the distribution of arterial involvement in this disease, based on a nationwide survey carried out in 1993. A total of 825 TAO patients with complete records were analyzed. There were 749 men and 76 women, with a mean age of 50.8 +/- 0.4 years. The survey assessed clinical manifestations categorized by Fontaine's classification, distribution of the lesions, associated diseases, responses to treatment, and outcome. This study focused on the distribution of arterial involvement. There were 42 patients (5.1%) with upper-extremity arterial involvement only, 616 (74.7%) with lower-extremity involvement only, and 167 (20.2%) with both. The most frequently affected arteries were the anterior (41.4%) or posterior (40.4%) tibial arteries in the lower extremities, and the ulnar artery (11.5%) in the upper extremities. There were no significant differences in the distribution of arterial involvement between men and women or between the right and left sides. In conclusion, approximately 25% of the patients had upper-extremity involvement. The anterior or posterior tibial arteries were most commonly affected. There was no significant difference in the distribution of arterial involvement between male and female patients.