Cytogenetic studies performed on 130 consecutive childhood acute non lymphoblastic leukemias (ANLL) and investigated in the same center between 1977 and 1986 have been studied for their prognostic value. Clonal chromosome changes were detected in 68.5% (89/130) of the cases prior to treatment. Complete remission rate and median survival were significantly lower in patients with only abnormal metaphases than in patients with only normal metaphases (NN) or a mixture of normal and abnormal mitoses (AN). The ANLL with translocation t(8;21), which were 58.6% of the M2 ANLL, were not associated with a particularly long survival (16 months) when compared with AN and NN ANLL. The longest survival (26 months) was observed in patients with acute myelomonocytic leukemia with bone marrow eosinophilia. Cytogenetic analysis have a prognostic value in childhood ANLL.