A 2-year-old Arabian filly, presented with the chief complaints of stallion like behavior and abnormal external genitalia present since birth. Examination revealed a cresty neck, a glans penis protruding from the clitoral fossa, and moderate mammary gland development. The patient had a blind-ended vestibule with the urethral papilla present on the ventral floor of the cranial vestibule, but no uterus or ovaries. The chromosomal sex of the patient was 64,XX. Blood estrogen and progesterone levels were consistent with a male or a mare in anestrus. An hCG stimulation test indicated that testicular tissue was present, but levels were more compatible with those of a cryptorchid stallion. The patient underwent laparoscopic gonadectomy, whereby gonads, both grossly and microscopically appearing to be testicles, were removed. The gonads were located at the entrance to the internal inguinal rings. The external genitalia was reconstructed into a more normal mare appearance. Following gonadectomy, the patient's clinical signs resolved.