The aim of this study was to document gender difference in aerobic capacity after cure from malignant disease in childhood. We studied 18 males and 17 females aged 11–19 years and 10–18 years, respectively. They had all completed their treatment at least two years previously. Twelve males and 11 females received anthracyclines in comparable doses (range 150–500 mg/m2). Maximal exercise tests were performed on a cycle ergometer. Maximal oxygen consumption (ml/min/kg) was significantly (p<0.001) lower only in females when compared to their controls. We postulate two causes: girls are smaller than their controls, possibly related to their higher vulnerability to cranial irradiation than boys; and girls were less involved than boys in sports. The influence of anthracycline treatment on aerobic capacity was only observed in males and not in females. This could be related to the higher exercise level in boys than in