Sex-linked muscular dystrophy associated with dystrophin deficiency has been reported in several breeds of dogs and is best characterized in the golden retriever. In this case report, a young, male Labrador retriever with dystrophin-deficient muscular dystrophy is presented. Clinical signs included generalized weakness, lingual hypertrophy, and dysphagia. Electromyographic abnormalities including complex repetitive discharges were present. Serum creatine kinase concentration was dramatically elevated. Histopathological changes within a muscle biopsy specimen confirmed a dystrophic myopathy, and dystrophin deficiency was demonstrated by immunohisto-chemical staining. While X-linked muscular dystrophy has not previously been reported in the Labrador retriever, a hereditary myopathy with an autosomal recessive mode of inheritance has been characterized. A correct diagnosis and classification of these two disorders are critical for breeders and owners since both the mode of inheritance and the prognosis differ.