Venous aneurysm can be classified into superficial or deep and secondary or primary. The aim of this study was to introduce primary venous aneurysm of the superficial venous system and to report the experiences treating it with sclerotherapy. A retrospective study with 120 cases of venous dilatation detects 4 patients. The clinical features, histopathology, and radiological findings were investigated. In 2 patients, sclerotherapy was performed. The patients had an asymptomatic, soft subcutaneous mass on the extremities or neck for 5.2 years on an average. Color duplex scanning showed a well-defined anechoic cystic structure with no arterial flow. Histopathologically, normal vein wall with varying degrees of thinning was observed. The patients who underwent sclerotherapy were treated successfully with no recurrence. Primary venous aneurysm of the superficial venous system should be included in the differential diagnosis of subcutaneous mass. In addition, it may be simply and effectively treated with sclerotherapy.