We conducted an epidemiological study of systemic sclerosis in the city of Tokyo using the records of patients who had been registered to receive free medical service for intractable diseases. A total of 636 patients were registered as having systemic sclerosis in 1987, and we sent questionnaires to the doctor of each patient. The contents of the questionnaires included the patient's name, sex, age, occupation, major symptoms, therapy and laboratory findings. We received 357 completed replies, and were able to analyse them. Our study estimated that at 1 January 1988 the prevalence rate in Japan was between 2.1 and 5.3 per 100,000. The male/female ratio was 14:1. The ages of the patients when surveyed ranged from 17 to 82 years, with a mean age of 51 years, peaking with the most numerous group being 50-59 years. The characteristic signs of systemic sclerosis were as follows: proximal scleroderma, 75%; sclerodactyly, 91%; pitting scars, 49%; short sublingual frenulum, 49%; pulmonary fibrosis, 45%; diffuse pigmentation, 45%; and phalangeal contracture, 35%. Raynaud's phenomenon was present in 93% of patients, and was the initial symptom in 59% of cases. With respect to specific antinuclear antibodies, anticentromere antibody was present in 19% and antitopoisomerase I antibody was present in 27%.