Uterine serosal inclusion cysts are structures derived from mesothelial cells attached to the uterus’ antimesometrial side and are mainly present in females during the postpartum period. They are physiologically inactive and do not interfere with reproductive functioning of the affected animals. It is typically an incidental finding in laparotomy and can be considered as a differential diagnosis when there is evidence of uterine content during abdominal sonography. Although it is not regarded as a pathology that affects animal welfare, its primary therapy is ovariohysterectomy. Case report: A 12-year-old mixed-breed bitch was presented at the Animal Reproduction Clinic of the Universidad Nacional de Colombia. The reason for consultation was abdominal distension, vulvar discharge, polydipsia, polyuria, and excessive vulvar licking. The diagnosis included clinical findings compatible with estrus, vaginal cytology indicative of estrus, uterine contents observed by sonography, and high serum progesterone levels. Hence, ovariohysterectomy therapy was recommended and performed. After surgery, a small amount of dark content was present in the uterine cavity along with anovulatory follicles, and as an incidental finding, several uterine serosal inclusion cysts were detected during the procedure. Conclusion: The presentation of this pathology is rare in nulliparous bitches, but it is of vital importance to consider it as a differential diagnosis in patients with signs of estrus and findings compatible with uterine content on sonography.