Of the congenital vascular abnormalities, venous malformations receive little attention and essentially no discussion of treatment. The author describes a 30-year experience with sclerotherapy, which was used for 34 venous malformations. In some cases, these lesions are localized and can be excised, but all the patients in this series had such extensive involvement of adjacent organ systems that no other treatment than sclerotherapy was tenable. Five patients had Klippel-Trenaunay Syndrome, five had head and neck involvement, two had involvement of the entire left side and the remainder had other areas affected. Sodium morrhuate, ethanolamine, sotradecol, and absolute ethyl alcohol were the sclerosing agents used. A butterfly needle was inserted into an anomalous vein, and a three-way stopcock connected to saline and the sclerosing solution was used to ensure intraluminal injection. When rapid runoff into normal venous tributaries could be a concern, a venogram on the operating table preceded injection of the sclerosing solution. Small lesions required only one treatment; widespread bulky lesions required more than 30 injections. The volume of sclerosing solution varied from 5 to 90 mL per injection course. Because of pain, general anesthesia and an overnight hospital stay were necessary. Patients with pharyngeal and/or laryngeal involvement required preliminary tracheostomy or endotracheal ventilatory support for 3 days. Complications included skin necrosis, transient nerve palsy, hemoglobinuria, and one case of anaphylaxis. Repeated aggressive treatment was required for the very large malformations because recanalization occurred. All the patients have been very satisfied with the results.