In order to determine the nature of infectious complications in hairy-cell leukemia we studied 20 consecutive patients seen at UCLA and analyzed the available literature. The incidence of serious infection in our series was 40%, and pneumonia and septicemia due to Pseudomonas and E. coli organisms were the leading types of infections. Fungal infections with Cryptococci and Histoplasma organisms were documented, and a single case of Pneumocystis carinii pneumonia was observed. Noninfectious fever occurred in 30% of our patients. There was a clear relationship between fungal disease and corticosteroid therapy, and the overall incidence of infection was correlated with the degree of neutropenia and corticosteroid treatment. No relationship was found between age, duration of disease, or the use of cytotoxic chemotherapy and infectious complications. Of the 13 infectious episodes, 11 occurred in patients prior to splenectomy. Only two episodes were seen in splenectomized patients, both occurring in the immediate postoperative period. We conclude that splenectomy has a beneficial effect in reducing the incidence of infections in hairy-cell leukemia and that corticosteroids should be used cautiously, since they predispose to opportunistic infection in this disease.