This module covers the duplex ultrasound of upper and lower extremity veins. Grey-scale image characteristics for normal veins are reviewed as well as diagnostic criteria pertaining to acute and chronic residual thrombus is discussed. Spectral and color Doppler features for both normal and disease states are described. Cases with various types of vascular pathology including acute thrombus, chronic residual thrombus and venous insufficiency are presented. Examples of other common non-vascular pathology that can be encountered during extremity venous ultrasound exams are also provided.