Two hundred and forty-four untreated acute myelogenous leukemia (AML) patients with unfavorable karyotypes and 109 others with favorable aneuploid karyotypes were used to evaluate the prognostic significance of having both normal and abnormal metaphases (AN) vs only abnormal metaphases (AA) at AML presentation. The AA and AN groups were similar with respect to known prognostic variables. Among patients with unfavorable karyotypes (-5, 5q-, -7, 7q-, and +8), the AN group had a significantly higher complete remission (CR) rate (46 vs 31%, P = 0.02), and a longer CR duration (P = 0.02) and survival (P = 0.026) than the AA group. The number of patients with other unfavorable karyotypes, such as t(11q23), were too small to evaluate properly. Among those with favorable karyotypes (inv(16) and t(8;21)), on the other hand, both the AN and AA group had similar CR rate, CR duration, and survival. Similarly, in patients with t(15;17), CR duration of the AN and AA groups were similar. These data suggest that, among patients with abnormal karyotypes, residual normal metaphases are associated with a higher CR rate, CR duration and survival, only in patients with unfavourable karyotypes, but not in those with favorable karyotypes.