Early screening is essential to counsel schoolchildren with congenital colour vision deficiency (CVD) in determining their future career path and to advise teachers of the impact of CVD on classroom difficulties. Congenital CVD is an X-linked genetic abnormality relatively commonplace in humans. This study aimed to determine the prevalence of congenital CVD in the Republic of Ireland schoolchildren and associated socio-demographic factors. A total of 1,626 schoolchildren (882 boys and 744 girls), in two age groups (728 aged 6-7-years and 898 aged 12-13-years) were examined from randomly selected schools. Colour vision testing was carried out using the Richmond Hardy-Rand-Rittler pseudoisochromatic test for colour vision (fourth edition); diagnostic plates were used to determine CVD type and extent if participants failed to identify symbols on the screening plates. CVD was detected in 73 boys (8.3 per cent, 95% confidence interval (CI) 6.6-10.3) and in 13 girls (1.8 per cent, 95% CI 1.0-3.1, p < 0.001). As expected, deutan (boys 4.8 per cent, girls 0.8 per cent) was the most common type of CVD, followed by protan (boys 1.7 per cent, girls 0.1 per cent), unclassified red/green CVD (boys 1.2 per cent, girls 0.8 per cent) and then tritan (boys 0.5 per cent). One case of achromatopsia was detected based on failure on all diagnostic plates. Traveller participants (boys 21.0 per cent, girls 8.6 per cent) had a higher CVD prevalence than their White non-Traveller (boys 7.2 per cent, girls 1.0 per cent) and non-White (boys 5.4 per cent, girls 1.1 per cent) counterparts (odds ratio 3.00, 95% CI 1.1-8.1, p = 0.006). In boys, CVD was also associated with twin birth (odds ratio 2.7, 95% CI 1.1-6.7, p = 0.03) and low birthweight (p = 0.04). This investigation of CVD in the Republic of Ireland schoolchildren should alert clinicians to the association between CVD and Traveller ethnicity, twin birth and lower birthweight. The prevalence of CVD found was similar to previous studies involving predominantly White populations and higher among Traveller participants; hence, counselling regarding inherited anomalies in the Traveller community is recommended. Early screening is essential to counsel schoolchildren with CVD in determining their future career path and to advise teachers of the impact of CVD on classroom difficulties.