Hairy cell leukemia (HCL) is a rare chronic B cell lymphoproliferative disorder that affects mostly men. It usually presents with pancytopenia, splenomegaly and bone marrow infiltration, without lymphadenopathy. Diagnosis is based on the presence of mononuclear cells with cytoplasmic projections in a blood smear, the typical bone marrow infiltration pattern and the immunophenotypic profile. HCL occurs seldom in young women and even more exceptionally during pregnancy. We report a 31-year-old woman in whom a splenomegaly was detected during routine prenatal care. Pancytopenia with 25% of hairy cells was found in her blood count. The patient was subjected to an open splenectomy and had an uneventful pregnancy. After two years of follow up, she has a normal blood count and has not required chemotherapy.