Lymphatic malformations (LMs) arise from abnormal development of lymphatic vasculature. Primary lymphedema is considered a form of LM. Recently, results in the investigators' laboratory demonstrated that propranolol, a pan beta-adrenergic receptor (βAR) antagonist, had cytotoxic and anti-proliferative effects against cells isolated from LM tissues. Preliminary results from treating symptomatic LM patients with propranolol at a dose range from 0.7-1mg/kg/day demonstrated a 70% positive response rate, with patients reporting improvement in their symptoms.