Thirty patients who had hemophilia and were seropositive for the human immunodeficiency virus were evaluated. The preoperative CD4 lymphocyte count was decreased to an average of 336 x 10(9) per liter (range, 27 to 708 x 10(9) per liter). After twenty-six orthopaedic operations in patients who had no previous bacterial infection, a nosocomial infection (cellulitis in the forearm, at the site of an intravenous catheter) developed in only one patient, but five patients had an abnormal postoperative fever that was not accompanied by the expected increase in the white blood-cell count. The preoperative CD4 lymphocyte count was significantly reduced in the patients who had an abnormal elevation in body temperature (p less than 0.004). The functional result or outcome after operation was similar to that in hemophilic patients treated before 1982. Subsequent progression of infection with the human immunodeficiency virus, as determined by the CD4 lymphocyte count and the Walter Reed classification system, occurred in most patients. Acquired immunodeficiency syndrome was diagnosed in six patients. A more rapid progression to acquired immunodeficiency syndrome was seen in the patients who had a lower CD4 lymphocyte count preoperatively. Preoperative evaluation of the CD4 lymphocyte count and the response to intradermal skin-test antigens in patients who are at risk for infection postoperatively provides additional information concerning immunological competence. With these data, the possible risk of infection in patients who are seropositive for the human immunodeficiency virus can be estimated more accurately.