Description: A 2-year-old Labrador Retriever bitch, was admitted to the Veterinary Clinical Service because of anoestrus. A chromosome investigation was performed using the lymphocyte culture method. Three copies of the X chromosome were identified in all the cells analysed. Besides the primary anoestrus, a chronic dermatitis was observed and abnormal behavior as coprophagy of cat and dog excrement. In all species with X-trisomy, either normal females or females with reproductive problems are involved. The phenotypic and clinical effects of X-trisomy are discussed