We compared the frequency of clinical features of systemic lupus erythematosus (SLE) and determined survival in 113 patients with younger-onset lupus (age less than 55 at clinical diagnosis) and 25 patients with older-onset disease (age greater than or equal to 55 at diagnosis). The most striking difference was in the racial distribution; 59% of the younger patients were black, compared with only 20% of the older-onset patients (P less than 0.001). Major manifestation of lupus (including clinically evident renal disease, central nervous system involvement, cutaneous involvement, and hemocytopenia) occurred with similar frequency in both age groups. Antibodies to DNA were detectable equally often in both groups, but hypocomplementemia was more common in the younger patients. Five-year survival in the younger-onset group (79%) was similar to that of the older-onset group (72%); there was a tendency toward relatively improved survival in patients survival of appropriately matched control populations. Major significant differences in racial distribution included 1) a higher incidence of serositis in older whites and in blacks regardless of age, and 2) more frequent hypocomplementemia in younger patients within both racial groups.