Splenic marginal zone lymphoma is a recently described primary splenic lymphoproliferative disorder that mainly affects older individuals. We report the case of a 22-year-old woman with morphologic and immunophenotypic findings consistent with splenic marginal zone lymphoma. This woman is one of the youngest patients ever described with this disease. The patient presented with complaints of left-sided abdominal fullness and was noted to have splenomegaly on physical examination. Laboratory evaluation revealed pancytopenia and a serum M component. The spleen was removed and weighed 1550 g. Histology showed prominent white pulp with an expanded marginal zone. The neoplastic cells were marginal zone-type cells with small to intermediate-sized nuclei with occasional conspicuous nucleoli and moderate amounts of pale to amphophilic cytoplasm. Immunophenotypic analysis revealed a B-cell population (CD20 positive) with kappa-light-chain restriction. The patient was treated with adjuvant therapy, but developed progressive disease less than 2 years after initial diagnosis.