Calf veins are one of the most common sites for deep vein thrombosis (DVT) but the management of patients with calf vein thrombosis differs. Many centres consider pharmacological treatment unnecessary and elect not to examine the calf veins with duplex ultrasound. Others advocate monitoring the thrombus with serial venous duplex scanning and commence treatment if there is evidence of propagation. In this laboratory duplex scanning of the calf veins is routinely carried out as part of the diagnostic procedure for DVT. A study was carried out where 50 patients with isolated calf vein thrombosis were followed over a one year period to determine the long term outcome in the calf veins. Note was made of the choice of treatment. A high percentage (85%) were treated with heparin/warfarin and only 15% received no pharmacological treatment. There was a propagation rate of 15%, one of which resulted in a fatal pulmonary embolus (PE). The DVT recurrence rate was 14% within the year. No long term effects such as valvular damage were noted during the follow-up period. The results suggest the need for better guidelines for the diagnosis and treatment of isolated calf vein thrombosis. Future studies with larger groups of patients need to be carried out to determine the significance of the recurrence rate and the long term effects. Duplex scanning enhances the diagnosis of calf vein thrombosis and should be used for closer observation of potential thrombus propagation.