Renal involvement or "scleroderma renal crisis" developed in 60 patients with progressive systemic sclerosis evaluated at the University of Pittsburgh during the period from 1972 to 1982. Forty-seven of these patients had progressive systemic sclerosis with diffuse scleroderma, representing 18 percent of persons with progressive systemic sclerosis and diffuse scleroderma evaluated during this time period. Ten additional patients did not have truncal scleroderma but were suspected of having incompletely developed diffuse scleroderma. Only three patients were classified as having progressive systemic sclerosis with the CREST syndrome. Renal crisis was observed early in the course of the illness, a mean of 3.2 years after onset. During May and June, this complication developed in fewer patients than expected. Thirty-six patients who had diffuse scleroderma and renal involvement after their initial Pittsburgh evaluation were compared with 212 who had diffuse scleroderma without renal involvement during follow-up. The patients with renal involvement had a shorter mean disease duration at the time of their first evaluation (2.4 versus 4.2 years, p less than 0.05) and less frequently had digital pitting scars (29 versus 54 percent), but no other significant clinical, laboratory, or serologic differences were noted. Data available for 31 patients with renal involvement during the six months preceding the onset of renal disease were analyzed. Blood pressure, serum creatinine, urine protein and red blood cells, and plasma renin levels were similar in these patients and the 212 patients without renal involvement. More patients with renal involvement had anemia or clinical evidence of cardiac involvement during this period compared with the patients without renal involvement. During the 12-month period prior to renal involvement, seven of 16 (44 percent) patients with such involvement had an impressive increase in skin thickening on physical examination compared with only 23 of 180 (14 percent) patients without renal involvement at any time during their course. Thus, the subset of patients with diffuse scleroderma who show rapid progression of their skin thickening early in the illness with development of anemia, pericardial effusion, or congestive heart failure have a high risk of "scleroderma renal crisis."