The vas deferens is infrequently palpated at the time of routine physical examination or even during examination of the scrotum. Its absence, especially unilaterally, has been associated both clinically and at the time of autopsy with ipsilateral renal anomalies, especially agenesis. Twenty-six patients with unilateral agenesis of the vas deferens were examined for the presence of an ipsilateral renal unit; 25 patients were examined by intravenous pyelography and one by bone scan. Twenty-two patients were missing the ipsilateral renal unit. Contralateral abnormalities occurred in seven (33%) of these 22 patients also. The absence of the vas deferens is a significant anomaly, and examination for the presence of the ipsilateral renal unit is mandatory.