Twenty pediatricians conducted a study for the detection of ophtalmological defects in children aged 36 to 54 months using a protocol designed by the Groupe Romand d'Etudes en Pédiatrie Ambulatoire (GREPA) and by an ophthalmologist. After a pilot test run for correcting the protocol and the testing procedure, visual acuity was assessed using the Scholatest, stereoscopy using the Lang test and ocular deviation using the Hirschberg test. A total number of 1243 children were examined, some of which needed to be tested twice. The visual acuity assessment provided an abnormal result in 241/1387 tests (17.4%); stereoscopy defects were detected in 39/1371 tests (2.8%) and strabismus in 41/1446 tests (5.7%). The test system allowed for detection of ophtalmological abnormalities in 14.7% of all children. This first Swiss study on detection of ophtalmological defects in preschool age children has established the feasibility of the testing procedure in ambulatory pediatrics during a routine examination. This procedure allows earlier detection of defects as well as earlier treatment with a better outcome. Early detection of ophtalmological defects has obvious Public Health implications.