Ocular opacity, associated with reluctance to move and inability to feed properly, was observed in approximately 1% of all newly hatched females from several related flocks of Mulard ducks. A 5-week follow-up study of 10 1-day-old affected females was performed, and they were compared with 10 control animals. Clinical, ocular and ultrasonographic examinations, and a complete necropsy of two animals per group with histological examination of the eye, were performed weekly. A bilateral immature cortical anterior cataract was diagnosed at ocular examination and confirmed by ultrasonography in affected ducks. Dyscoria was occasionally observed in affected animals. Severe cataract, with Morgagnian globules, severe anterior fibre liquefaction and disorganization were observed by photonic microscopy. No retinal or choroidal lesions were observed. No progression or repair of ultrasonographic and microscopic lesions could be detected during the 5 weeks of examination. The female predisposition for the ocular lesions suggests a congenital sex-linked recessive cataract.