Real-time ultrasonography (US) was used as a single non-invasive method in the management of 174 patients (56 inpatients and 118 outpatients) with suspected deep-vein thrombosis (DVT). Therapeutic decisions were based on the results of ultrasonography alone. If the US examination was abnormal anticoagulant treatment was started. If the initial US examination was normal, no treatment was given and the patient underwent repeated testing and physical examination after 1 day, 7 days and 3 months. In the outpatient group, 1.3% of the ultrasonographic negative patients developed thromboembolic complications (95% confidence limits, 0.03-7.21%). None of the initial ultrasonographic negative patients developed proximal DVT after 1 day and 7 days. In the inpatient group, 10% of the ultrasonographic negative patients developed thromboembolic complications (95% confidence limits, 1.2-31.7%). In 18% of the ultrasonographic negative patients an alternative, unexpected diagnosis was obtained by ultrasound. The most frequent alternative diagnosis was a popliteal cyst. The results indicate that US alone appears to be a safe diagnostic method in the management of outpatients with suspected DVT. In the inpatient group further research is required for definite recommendations regarding a safe ultrasound follow-up schedule.