Eleven patients with congenital esotropia were tested with the Bayley Scales of Infant Development (BSID) before surgery and at two and six months after surgery. Eight patients completed all three tests and no obvious changes were found between the first and last test. Of the eight patients, two were considered developmentally normal by the BSID; three had significantly delayed mental and motor scores; one showed significant mental delay; and one had motor delay. Medial rectus muscle recessions were done bilaterally on all patients. Four required a second operation. Orthophoria was obtained in six patients.