We searched Medline, Pascal, and Current Contents for literature on the treatment of hairy cell leukemia over the last 10 years and discuss here available data on response rate, mechanism of action and adverse effects of different therapeutic options. BY TREATMENT: Interferon generally induces partial response and most patients relapse after treatment withdrawal. The purine analogs, desoxycoformycine and 2-chlorodeoxyadenosine, are more active than interferon inducing response in approximately 90% of the cases, even after interferon failure, complete response is achieved in 50% to 70% of patients. Relapse rate at 5 years appears to be limited to 10% n 15%. Besides infections, the main adverse effect is the constant deep and persistent decline in CD4 counts but with no special risk of opportunistic infection. The increased rate of secondary cancers in long-term survivors and its possible relationship with treatments remains a controversial topic.