Klippel-Trénaunay-Weber syndrome is diagnosed with at least two of these three features are present: capillary malformations, soft tissue or bone hypertrophy, and varices or venous malformations. Most cases are sporadic. Most cases involve the lower limb as the site of malformations. 

These patients are at risk for sequestration of platelets, resulting in Kasabach-Merritt syndrome (a consumptive coagulopathy). They can also suffer from stasis dermatitis, thrombophlebitis, cellulitis, congestive heart failure, bleeding, and thromboembolic events.