Introduction: X-linked recessive hereditary disorders is the main cause of colour vision deficiency (CVD). The prevalence of CVD varies from race to race. This study was conducted to determine the prevalence of CVD among 10-to16-year-old school children in Galle educational zone, Sri Lanka.Methods: A total of 566 students (males = 260) were examined with Ishihara pseudo-isochromatic colour plates. The parental questionnaire was used to obtain a family history of CVD, the ability of the child to select coloured objects and past medical history. Both parents and children were subjected to the same questions separately on their ability to differentiate coloured objects during activities of day-to-day life. Parents reported difficulties and child reported difficulties in colour perception were compared with 32 healthy age matched controls who were selected from the same school of the respective CVD patients. Results:The overall prevalence of CVD was 1.4% with a prevalence of 3.1% for males. Patients were detected in all three main ethnic groups of Sri Lanka (Six Sinhala, one Tamil and one Muslim boy). All affected children had negative histories of previous systemic and ocular disease or chronic use of medications. The visual acuity and the ocular fundi were normal in all affected children. Seven (1.23%) had deuteranomaly, while one (0.17%) had protanomaly. Seventy five percent (06) of the parents of affected children were unaware of their child's defect, while only one reported a positive family history. Parental reporting of difficulties in selecting coloured objects in the child's day-to-day activities was not significantly associated with the defect (p>0.05). Children with CVD had reported difficulties in identifying colour objects in television/computer programmes and separation of cooked from uncooked food (p<0.05). Fifty percent of the affected children were intimidated by their friends for their difficulties.Conclusions: CVD is not uncommon in the Galle education zone, Sri Lanka. The affected children face difficulties in their day-to-day life due to their defects.