['The expression of CD56 is considered a bad prognostic factor for overall survival, lower rates or short complete remission and extramedullary invasion but the results are controversial. The importance of validating new prognostic parameters in acute leukemias was the reason to investigate the CD56 expression in blast cells of patients with acute myeloid leukemia.', 'A cohort of 48 patients treated at Hospital de Clinicas de Porto Alegre and diagnosed with acute myeloid leukemia as classified by the French-American-British group (FAB) criteria using cell morphology, cytochemistry and flow cytometry were evaluated.', 'Eight cases (16.7%) were CD56 positive without correlation to age or gender. The highest incidence of CD56 positivity was in FAB subtypes M4 and M5. The death rate during induction was not significantly different between patients with and without CD56 expression (62.5% vs. 27.5%; p-value = 0.097). However, patients that expressed CD56 had significantly lower overall survival than those who did not (mean 4.0 months vs. 14.5 months; p-value = 0.03).'] Is the expression of CD56 antigen associated with poor prognosis in patients with acute myeloid leukemia?