Suspicion of deep venous thrombosis (DVT) is a common reason for acute medical admission. The clinical diagnosis is difficult, and thus significant numbers are investigated and found to be normal. Provision of 24-h radiology is costly, and there may be a delay in investigation. We assessed computer-assisted venous occlusion plethysmography as a screening test for DVT, compared with standard radiology. The test has the advantage of being performed on the ward and if reliable would significantly reduce the number of radiological investigations required. We enrolled 215 consecutive patients presenting with the possible diagnosis of DVT, of whom 144 had technically adequate plethysmography results. Plethysmography had a sensitivity of 96% (95%CI 88-99%) and a negative predictive value of 97% (95%CI 91-99%). Patients excluded because of technically inadequate results were older (by a mean 7 years, p=0. 003). Computer-assisted venous occlusion plethysmography is a non-invasive method of rapidly screening for DVT which may be safely used as an initial screening test. The test is less useful in older patients, or patients unable to keep still for a period of 2 min.