Bladder prolapse is a rare condition in mares and may occur as a result of excessive straining during the parturition or in the postpartum period. We report a case of dystocia associated prolapse and incarceration of the small colon through the external urethral opening into a prolapsed urinary bladder. No previous reports of this condition were found. An 11-year-old Thoroughbred mare was presented to The Equine Hospital at the Jockey Club of Saudi Arabia for evaluation and treatment of dystocia. Prolapse of the urinary bladder was concomitantly diagnosed. Initial assessment deemed replacement of the urinary bladder in the normal position and vaginal delivery not possible. The mare was immediately prepared for caesarean section. The foal was successfully delivered and resuscitated. Detailed assessment of the bladder during the surgery revealed that the small colon had prolapsed through the external urethral opening and was inside the bladder. The urinary bladder was opened. The small colon was replaced into the abdominal cavity; a first surgeon gently replaced the small colon through the external urethral sphincter and a second surgeon retrieved the small colon by gentle traction. The mare recovered uneventfully from general anaesthesia. The mare and the foal were discharged from the hospital seventeen days post-operatively.