Lymphatic malformations (LMs) in soft tissues tend to enlarge over time, causing distortion, obstruction, and functional problems. The purpose of this study was to determine the natural progression of LMs to facilitate patient counseling, gain insight into pathophysiology, and guide therapy. Our Vascular Anomalies Center database was reviewed for patients with cutaneous and soft tissue LMs; combined or visceral lesions were excluded. Predictive variables were age, channel type (macrocystic, microcystic, combined), sex, lesion size (localized, diffuse), and location (head/neck, extremities, trunk). The outcome variable was natural progression of the malformation defined by expansion or the onset/worsening of signs and symptoms. The study included 441 patients: 234 females (53.1%) and 207 males (46.9%). Lymphatic malformations were located in the head/neck (61.2%), extremities (17.5%), trunk (16.1%), or multiple sites (5.2%). Children had a 42.2% risk of progression before adolescence, 84.7% before adulthood, and 95.3% during their lifetime. Progression was more likely in adolescence (63.8%) than in childhood (40.8%); the odds ratio was 2.6 (P=0.003). Diffuse LMs worsened more often than localized lesions (P=0.001), whereas channel type (P=0.63), sex (P=0.42), and location (P=0.28) did not influence progression.Lymphatic malformations have a greater risk of progression in adolescence than in childhood; pubertal hormones may contribute to expansion. Because of this high rate of progression, early treatment of asymptomatic LMs should be considered.