The present study is a detailed analysis of the cytogenetic features of leukemic cells from 104 immunologically classified acute lymphoblastic leukemia (ALL) (78 B lineage and 26 T lineage) cases. Clonal chromosomal abnormalities were found in marrow blasts from 77 of 104 (74%) cases. Hyperdiploidy was much more frequent in B-lineage ALL cases, whereas normal diploidy was more common in T-lineage ALL cases. Fifty-nine of 104 cases (46 of 78 B-lineage ALL and 13 of 26 T-lineage ALL cases) had structural chromosomal abnormalities. Structural abnormalities involving 2p11, 7p13, 7p22, proximal q arm of 7 (7q11 or 7q22), 11q23–24, and translocations involving 12p11–13 appeared to be B- lineage specific. By comparison, structural abnormalities involving 7p15, 7q32, and 14q11 displayed T-lineage specificity. Structural abnormalities involving 9p22-p23 or 14q32, del (6)(q21-q23), del (12)(p11-p13), and the Philadelphia chromosome were found in B-lineage as well as T-lineage ALL cases. This study expands the current knowledge about immunophenotype-karyotype associations in ALL.