1829 school-boys of Singapore comprised of 849 Chinese, 469 Malays and 511 Indians were investigated for the incidence of red-green colour-blindness with Ishihara's plates. The incidence of red-green colour-blindness was found to be 3.8%, 4.5% and 4.5%, respectively in Chinese, Malay and Indian boys. The incidence among the different dialect groups was variable with the highest incidence of red-green colour-blindness among Mandarin speaking group (14.3%), followed by Hainanese speaking (6.7%) and other dialect groups of Chinese (2.8% to 4.5%). The incidence of red-green colour-blindness was higher in the older boys compared with the younger boys when all the three ethnic groups are combined.