OBJECTIVE To determine the causes and prevalence of ocular morbidity among primary school children in Ilorin, Nigeria. METHODS A cross sectional survey of primary school children in 10 randomly selected primary schools within Ilorin, Nigeria was carried out between July 2005 and January 2006. Relevant ocular history and basic ocular examinations were carried out on the children that were selected from a multi-stage sampling process. RESULTS One thousand three hundred and ninety three pupils were surveyed. There were 689 (49.4%) boys and 704 (50.6%) girls. The age range was between 4 and 15 years. The mean and modal ages were 10.16 SD 2.5 and 10 respectively. Two hundred and seventy seven pupils had ocular pathology giving a prevalence of 19.9%. The two most common ocular disorders found among the pupils were refractive errors and vernal conjunctivitis with prevalence of 6.9% and 6.7% respectively. Others included genetic / congenital / developmental ocular disorders 39 (2.8%), glaucoma / glaucoma suspect 20 (1.4%), ocular infections 18 (1.3%), and ocular trauma 11 (0.8%). More than three-quarters (86.7%) of the causes of visual impairment and blindness among the pupils were avoidable (preventable or treatable). CONCLUSIONS The sheer magnitude of avoidable causes of visual impairment and blindness in the study underscores the need for effective school eye-health programmes in developing countries.