Controversy exists as to whether patients suspected of having deep vein thrombosis (DVT) can be studied safely without venography, with its attendant expense, inconvenience, and potential risk. We used impedance plethysmography (IPG) in 1,464 consecutive patients suspected of having DVT, with 96% of these patients with normal IPGs, there were no fatal pulmonary emboli (PE). The incidence of nonfatal PE was 1%. In 284 outpatients suspected of having DVT, but discharged without treatment because of normal IPGs, only one patient returned with subsequent symptoms of DVT (0.4%). Noninvasive testing with IPG is a safe and highly cost-effective alternative to venography for routine management of patients suspected of DVT.