We analyzed by immunocytochemistry the expression of survivin in bone marrow cells from 36 acute myeloid leukemia (AML) cases, from 98 patients with myelodysplastic syndrome (MDS), and from 41 non hemopathic subjects. Our aim was to evaluate whether abnormalites in survivin expression were associated with peculiar laboratory and clinical findings, altered apoptosis levels or altered proliferative rate. In normal samples survivin was never detectable. It was detected in almost all AML and MDS cases. In AML and in MDS with more than 5% bone marrow blasts survivin levels higher than in RA and RARS were observed (P=0.04). In MDS a tendential inverse correlation between survivin and TUNEL positivity was identified (P=0.08), whereas survivin expression was independent of the proliferative rate. Survivin levels did not predict disease progression in MDS; among AML patients treated with intensive polichemotherapy, survivin expression was significantly higher in resistant cases (P=0.01). Our findings confirm the high incidence of survivin expression in AML. Its abnormal expression also in MDS may play a role in promoting aberrantly increased cell viability and contribute to the altered homeostatic balance between cell growth and cell death.