The mental and intellectual development of 75 children aged 6 to 10 years who had undergone operations during their neonatal period was estimated using the WISC-R intelligence test and the Bender-Gestalt test (BGT). WISC-R test results correlated with patients' total surgical stress scores, number of operations, and total duration of hospitalization. A tendency for verbal IQ deficiency was observed in many patients. BGT results correlated with the number of operations and total period of hospitalization. Patients with anorectal anomalies were apparently affected more than those with other diseases. An accumulation of therapeutic stresses relating to operations and hospitalizations during childhood extending through the neonatal period may affect subsequent mental and intellectual development.