In 96 cases of childhood acute lymphoblastic leukemia (ALL), handmirror cells (HMCs) were counted in cytospin preparations of washed lymphoblasts obtained at diagnosis. HMC counts were significantly lower in T-ALL as compared to C-ALL (p less than 0.001). In T-ALL and pre-T-ALL 2/35 cases had more than 10% HMCs; in C-ALL 22/41 cases had more than 10% HMCs. In two cases of B-ALL 19% and 36% HMCs were found. Thus, HMC expression in ALL is related to the immunological phenotype, especially found in ALLs originating along the B-cell lineage.