The incidence of red-green colour vision defects was studied in a sample of 392 
Basque students (174 males and 218 females), using the Ishihara test cards 
(1987). The frequency of red-green colour blindness was 4.02 percent in the 
males and 0.46 percent in the females. The colour blindness frequencies found 
among males are within the range of other Spanish samples. Nevertheless they are 
lower than the values reported in other European populations.