The causes of death were examined in patients with systemic lupus erythematosus (SLE) who were cared for at the University of California, San Francisco and who died after 1969. Of the 44 deaths analyzed, 33 patients had autopsies. Infections were common and often determined to be the cause of death. Overall, infections were present in 55 percent (22/44), and judged to be a cause of death in 30 percent (13/44) of all deaths. The infections could be divided into 2 groups: those due to common bacterial organisms and those due to opportunistic infections. These two types of infections occurred with similar frequency. When compared to common bacterial infections, however, the opportunistic infections were more likely to be first diagnosed at autopsy (p = .001). In only 3 of the 15 patients with an opportunistic infection was the diagnosis made antemortem. Failure to diagnose an opportunistic infection early occurred when the infection simulated active SLE, and when the possibility of an opportunistic infection was not aggressively investigated. The most common opportunistic infections were Candida albicans and Pneumocystis carinii. The most common site of opportunistic infection was the lung. Seventeen patients had 27 common bacterial infections, chiefly sepsis from Staphylococcus aureus and aerobic gram-negative organisms. Eight patients had both a common bacterial and an opportunistic infection. Stepwise linear regression analysis showed that death from infection correlated most strongly with prednisone and cytotoxic drug use in the 3 months before final admission. No measure of lupus activity was found to correlate with death from infection, except that hypocomplementemia correlated with death from bacterial infections.(ABSTRACT TRUNCATED AT 250 WORDS)