In childhood acute lymphocytic leukemia (ALL), abnormalities in the short (p) arm of chromosome 9, particularly those leading to the loss of material in the p21-p22 region, may be associated with bulky disease at diagnosis (so-called 'lymphomatous' ALL) and a T cell immunophenotype. To assess these associations further, we reviewed the clinical and laboratory data for 100 consecutively evaluated children with ALL who had successful cytogenetic studies. From analysis of clinical and laboratory features, 8 of the 100 patients were classified as having lymphomatous ALL. Seven of the 100 patients had aberrations involving the 9p arm or were missing an entire chromosome 9. The prevalence rate of 9p abnormalities in cases of lymphomatous ALL was not significantly different from that in cases without lymphomatous features (1 of 8 v 6 of 92, P = .62). Moreover, all seven patients with 9p abnormalities had the common ALL phenotype. These data suggest that although 9p abnormalities in childhood ALL occur frequently, there is no consistent association with either the occurrence of lymphomatous clinical features or the presence of T cell disease.