HIV infection is commonly associated with cytopenias. The occurrence of erythrocytosis is rare, with only one report in the medical literature. We have described the case of an asymptomatic patient found to be seropositive for HIV. The blood counts were initially normal except for mild eosinophilia and thrombocytopenia. Over the next 18 months erythrocytosis developed and thrombocytopenia worsened. Workup at that time revealed elevated red cell mass, suppressed erythropoietin, normal arterial oxygen saturation, and splenomegaly documented by abdominal computed tomography. Zidovudine therapy was started in April 1990, when the CD4 cell count dropped below 500/mm3. Over the next 4 months the hematologic indexes returned to normal levels. The patient remains asymptomatic.