The results of ophthalmological and colour vision studies are reported on 13 patients from a family with a dominant cone dystrophy spanning seven generations. The onset of visual deterioration occurred in the third or fourth decade. In the early stages of the disease, when visual acuity is still close to normal, a severe defect in the blue sensitivity is already present, as measured by spectral sensitivity curves and other tests suitable for the detection of tritan defects. In our opinion this condition represents a distinct entity with autosomal dominant inheritance.