The prognostic significance of kidney size at diagnosis of acute lymphoblastic leukemia (ALL) was assessed in a population of 142 children. Kidney size was determined using three different methodologies, and its significance was determined by univariate and multivariate life-table methods. Enlarged kidney size (as determined by any of the three methods used) was not associated with an overall poorer survival. These findings were consistent when kidney size at diagnosis was analyzed as a singled variable and when it was considered after adjustment for the known prognostic factors of age, sex, and initial WBC count. Assessment of renal size at the time of diagnosis of childhood ALL is not indicated for the purpose of predicting subsequent prognosis.