Angiotensin converting enzyme (ACE) gene insertion(I)/deletion(D) polymorphism influences the outcome of a number of cardiovascular diseases. ACE I/D polymorphism was investigated by PCR in 207 pediatric cancer patients and 144 controls. ACE I/D distribution of patients and controls was similar. The frequency of the D allele and the prevalence of the deletion (DD) genotype were significantly (P < 0.05) higher among patients with severe circulatory compromise requiring treatment in the intensive care unit (ICU) than among the other patients and controls. Patients with the DD and ID genotypes spent significantly (P < 0.05) longer time in the ICU than patients with the II genotype.