This report describes the successful management of a pregnant 14-year-old seven-eighths Thoroughbred mare with an ovarian granulosa cell tumour. The mare initially presented with unilateral ovarian enlargement whilst being managed for artificial insemination, demonstrating normal ovarian function with ovulation from the contralateral ovary leading to conception. The mare subsequently re-presented with stallion-like behaviour at 3.5 months gestation and ovarian suppression was evident. The mare maintained her pregnancy and delivered a live colt foal at term. Ovariectomy was performed 3 months post foaling and the mare regained cyclic activity 9 months post surgery. The mare then conceived and became pregnant once more. The diagnostic and therapeutic challenges during pregnancy are discussed.