Lymphatic malformations have been rarely reported in literature either in humans or in animals. However, in recent years, concern about these malformations in humans has increased. A five-month-old Rasa Aragonesa male lamb was received at the Ovine Clinical Service of the Veterinary Faculty of Zaragoza, Spain, with a history of cervical protuberances coming from birth. The lamb showed three round swollen lumps (5–12 cm in diameter) parallel to the trachea on the left side of the neck. Clinical examination, haematology, ultrasonography, fluid examination and histopathology were performed. No abnormalities were found in blood samples and ultrasound confirmed a multicystic lesion with internal separations. Histological evaluation of the tissue revealed dilated lymphatic vessels and channels in the dermis and hypodermis; some lymphatic vessels were filled with amorphous proteinaceous material and occasional lymphocytes and macrophages. These protuberances were diagnosed as congenital lymphatic malformations. Most of the gross and microscopical lesions were very similar to those described in humans. To the authors’ knowledge, this is the first time that a congenital lymphatic malformation is described in sheep.