Interstitial deletion of the long arm of chromosome 9 (9q-) is an uncommon karyotypic abnormality in acute myeloid leukemia (AML). We report a case of acute myeloid leukemia, M6 according to the FAB criteria, in which 9q- was the sole karyotypic abnormality. From our own experience and that in the literature, interstitial 9q- seems to be associated with two specific morphologic/cytogenetic categories: AML M2 and t(8;21)(q22;q22)/trisomy 21; and as the sole karyotypic aberration in AML M1/M2(M6) with dyserythropoiesis. Examination of the published karyotypes shows that 9ql3 to 9q21 is the commonest deleted segment, suggesting that this region may carry genes important in leukemogenesis.