Diffuse systemic sclerosis and the related syndromes were diagnosed in 115 patients during 1977-1987. Sixty-nine patients were available for clinical evaluation and analysis. These included 46 patients with diffuse systemic sclerosis, 2 with limited cutaneous systemic sclerosis, 2 with linear scleroderma, 18 with overlap syndrome (OS), and one with primary Raynaud's disease. The major clinical manifestations among the diffuse scleroderma patients were the involvement of the following systems; cutaneous (93.3%), musculoskeletal (69.6%), gastrointestinal (54.3%), and pulmonary (43.3%) while renal involvement (4.3%) was less common. Antinuclear antibodies were found in 89.7% with predominating speckle pattern (86.2%) and anti Scl 70 antibody (40.6%). In contrast to the Western series, HLA-DR2 was significantly increased in our diffuse systemic sclerosis patients (p less than 0.01). Among the 18 OS patients, the involvement of pulmonary system (44.4%) was the major cause of morbidity and renal involvement (55.6%) was found frequently although it was clinically mild. In conclusion, our diffuse systemic sclerosis and related diseases patients seem to have milder clinical manifestations than those of the Western series.