Trisomy 8 is a relatively common finding in acute nonlymphoblastic leukemia (ANLL). In childhood acute lymphoblastic leukemia (ALL) it apparently is much more rare. Although Human Gene Mapping 11 included trisomy 8 as a marker for a subgroup of ALL, morphologic and immunologic characteristics of this entity have not been defined. We describe a case of early T-cell ALL (T-ALL) in a pediatric patient in whom this abnormality was the sole chromosome aberration. In situ hybridization with a chromosome 8-specific alpha-satellite DNA probe was performed. Our data are discussed and compared with pertinent literature.