The decision between continued medical therapy and surgical exploration in patients with complicated epididymitis is difficult. We evaluated scrotal ultrasonography as a noninvasive aid in such problematic cases. During a 48-month period 95 patients were hospitalized for treatment of epididymitis; 23 underwent scrotal ultrasonography and 10 required orchiectomy. Analysis of the 21 cases with abnormal findings demonstrated that orchiectomy was necessary in 1 of the 10 patients (10 per cent) with epididymal enlargement only, in 2 of 8 (25 per cent) with epididymal enlargement plus hypoechoic testes and in all 3 with epididymal enlargement plus testicular inhomogeneity (p equals 0.0099). Patients with progressive testicular changes on serial ultrasound examinations uniformly required orchiectomy (5 of 5). Sonographic findings of testicular inhomogeneity correlated with testicular infarction and findings of decreased testicular echogeneity correlated with acute or chronic orchitis. In the appropriate clinical setting gray scale ultrasonography provides objective information supporting the need for surgical intervention in selected patients with complicated epididymitis.