Forty seven children affected with acute lymphoblastic leukemia (ALL) were cytogenetically investigated at diagnosis and all through different stages of the disease (remission and relapse). A clonal karyotypic abnormality was found in 32% at diagnosis (mainly comprised of cALLa+). A hyperdiploid mode with chromosome counts ranging from 47-58, was found to be most prominent among cALLa+ patients. The most common numerical aberrations were gain of chromosomes 2, 5, and 21. The structural aberrations at diagnosis were found to be del(9)(p22), inv(9)(p11q13) and del(19)(p12). None of the children showed ph+ chromosome. A good prognosis was found in cALLa+ children with an abnormal karyotype at diagnosis and of these children, those who showed karyotypic instability, had a significantly longer first remission time. The karyotypic evolution through remission(s) and relapse(s) revealed the occurrence of structural alterations, including changes in chromosomes 3, 6, 9, 21 and 22. However, irrespective of the karyotypic clonal nature at diagnosis, chromosome 9 was the most commonly involved chromosome through the course of disease.