Deep venous thrombosis is a widely recognized medical problem which results in significant morbidity and mortality. Venography is the current 'gold standard' diagnostic test for deep venous thrombosis; however it is costly, invasive and is unnecessarily performed in 50% of cases. This paper describes a self-contained, non-invasive system for automatic venous occlusion plethysmographic measurement and analysis. An examination of 274 symptomatic limbs was conducted using strain gauge plethysmography and a subsequent venographic examination was then performed. The plethysmographic results were then compared with venography so as to develop a means of discrimination for thrombotic and non-thrombotic limbs. Strain gauge plethysmography using the Belfast DVT Screener yielded a sensitivity of 100% and a sensitivity of 66.3% for proximal segment DVT. The efficacy of the discriminatory algorithm was then tested for the diagnosis of DVT in a further 101 symptomatic patients. A sensitivity of 94.7% and a specificity of 81.7% were observed for strain gauge plethysmography for proximal segment thrombosis in this patient group. The Belfast DVT Screener is highly sensitive for deep venous thrombosis and may be used to reduce the need for venography, which is of benefit to both the patient and clinician.