An isochromosome 12p [i(12p)], typical of germ cell tumours (GCT), has, to date, been observed in 10 cases of acute myeloid leukaemia (AML) or myelodysplastic syndrome, nine of which had concurrent or preceding GCT. We report two i(12p)-positive AML cases without clinical evidence of GCT. One patient with AML-M1 had two i(12p) as the only cytogenetic anomalies. In the other case of AML-M3 with t(15;17)(q22;q11-12) at diagnosis, the i(12p) was clearly a secondary rearrangement since it first appeared at relapse and always accompanied the t(15;17). Our results suggest that i(12p) does not always indicate neoplastic disease of germ cell origin.