Venous insufficiency is characterized by poor function of the venous valves, resulting in an inability of blood to move at an adequate rate toward the heart. Other contributing factors include vessel wall inflammation, venous hypertension, and dysfunctional muscle (notably calf) or vascular pump mechanisms. Dysregulation of transforming growth factor beta 1 (TGF-ß1) expression, which can cause a shift in hemodynamic forces, wall inflammation, and extracellular matrix degradation / deposition, is thought to play a role in the development of venous insufficiency.

Veins of the lower extremities are most often affected. Superficial venous valve incompetence may be due to pre-existing weakness in the vessel wall or valve leaflets or from injury, superficial phlebitis, or venous distension from hormones or hypertension. Deep venous valve dysfunction is generally due to damage from previous deep vein thrombosis.

Common early findings in the legs include pain, pruritus, tingling, nocturnal cramping, and a sensation of "heavy legs." Symptoms are alleviated when legs are elevated. Later-stage findings include leg edema, skin changes, and ulceration. Other complications include thromboembolic events and superficial thrombophlebitis.

Venous insufficiency is quite common, with prevalence rates reported as high as 70% in women and around 55% in men in some studies. Risk factors include older age, female sex, familial history, tall height, pregnancy, obesity, prolonged standing, immobility, and sedentary lifestyle.