Here we report 3 cases of trisomy 11 observed in 1 patient with secondary acute myeloblastic leukaemia and in 2 patients with spontaneous acute myeloblastic leukaemia. In all 3 patients, the picture of overt acute leukaemia arose following a clinically established myelodysplastic syndrome. These findings, together with the previously reported occurrence of trisomy 11 in myelodysplastic syndrome and in acute myeloblastic leukaemia, suggest that this abnormality can be considered specifically associated with myelodysplastic syndrome and with the subsequent and related acute myeloblastic leukaemia.