Cystic lymphangiomas are birth defects affecting the lymphatic system. These are rare benign dysembryoplastic lesions predominate in the region of the head and neck, more particularly in the posterior cervical triangle. They usually occur in childhood and are exceptional in adults. The diagnosis is evoked by the clinic (lateral-cervical swelling) and imaging (ultrasound and tomodensitometry), then confirmed by histology after surgery which forms the basis of treatment. We report a case of cervicothoracic cystic lymphangioma in a patient of 45-year-old with a review of the literature.