A family with two achromatic members, a sister and brother, is described. Their parents were first cousins. Eye examination of the 34 relatives examined revealed no abnormalities in 32. The son of their youngest brother was deuteranomalous. However, since this recessive trait is X chromosome linked, this failure was not related to the achromatopsia gene. The granddaughter of their eldest brother had difficulties in colour vision tests and was interpreted as an anomalous trichromat of unclassified nature. This might be a slight intermediate heterozygotic manifestation of the gene. The information of those relatives not examined revealed only a deceased paternal aunt who had had poor vision of an unknown cause. Congenital achromatopsia is rare but nevertheless should be kept in mind in cases of unexplained amblyopia. The nature of this disorder justifies the opthalamologist to inform these patients of the hereditary character of this disease and to give advice on educational guidance to them.