The canine congenital anomalies of the uterus are rare. The segmental aplasia of uterine horn results from defects during the development of the segmental paramesonephric duct, where parts of the uterine horns may be absent, and only a small fibromuscular band may be present on the local. This anomaly is associated with intersex and inbreeding, but may also occur as a not genetic event. If the aplasia is unilateral, fertility is not necessarily impaired. A canine, female, Poodle, 3 years old, was presented to the Hospital of Veterinary Clinics, Federal University of Rio Grande do Sul, for an ovariosalpingohysterectomy procedure. In surgery the absence of the left uterine horn was notice, the right horn apparently normal, normal ovaries and uterine body. Histopathological examination diagnosed segmental aplasia of the left uterine horn and cystic endometrial hyperplasia in the right horn. Even with this change, the animal showed estrous cycles, which can be normal, even without the presence of one of the uterine horns, as the existing can be functional. The majority of congenital uterine anomalies are on the uterine horns. The segmental aplasia of uterine horn is rare and difficult to diagnosis without an invasive investigation. Normally, only detected in exploratory laparotomy or castrations. Histopathological examination is necessary so you can distinguish the type of anomaly. The urinary tract should be reviewed, too, because this may be affected.