In this study we report the observation of premature chromosome condensation (PCC) in two children with acute lymphocytic leukemia L1 and one child with malignant histiocytosis. Cytogenetic analysis was performed on peripheral blood or bone marrow cells cultivated for 24 hours without mitogen. In all three reported cases the modal karyotype was normal, while 12.9%, 5.5%, and 5% of spreads with PCC was observed, respectively.