About 50% of vascular malformations are located at the head and neck region where they can usually be associated with functional and/or aesthetic limitations. Laser treatment has proven to be effective in treatment of small low-flow vascular malformations, but little is known about the use of this therapy for high-flow larger arteriovenous malformations (AVMs). A congenital high-flow vascular malformation of the upper lip had to be treated because it was causing functional impairment and deformity which were affecting the quality of life. The mainstay of treatment is surgical therapy after embolization of the lesion, but the treatment of high-flow lesions is difficult because of the high risk of mortality and morbidity. The lesion was then treated with transmucosal diode laser applications in multiple sessions. The lesion progressively reduced in dimension without any sign of recurrence after multiple sessions of transmucosal diode laser applications. The clinical examination and the ultrasound scan performed four years after the last treatment demonstrated that no complications or further recurrence occurred. Multiple sessions of diode laser application can be a safe, effective and minimally-invasive treatment for oral mucosa vascular malformations, even if characterized by high flow.