We report three cases of trisomy 4 in acute leukemia. This alteration was detected as the sole cytogenetic abnormality in a case of FAB M4 leukemia; it occurred in association with 5q deletion in a case of M1, and concomitant with Ph chromosome and trisomy 17 in a case of L2 leukemia. The latter case represents the fourth report of trisomy 4 in acute lymphoblastic leukemia.