Congenital monoblastic leukemia cutis is a rare disorder. We report an infant who developed infiltrative skin lesions by 2 weeks of age, which, when biopsied at 4 1/2 months of age revealed a monoblastic infiltrate. Blasts in the peripheral blood were not seen until 1 week before her death at 8 months of age. Chromosomal analyses of her bone marrow showed an abnormal clone of cells with a 46,XX,del(10)(p12) karyotype. Although chromosome 10 is rarely involved in hematologic malignancies, abnormalities of this chromosome within the region 10p11-10p13 have now been shown in four of 10 reported cases of congenital monoblastic leukemia.