Subclinical varicocele represents an abnormality of veins of the pampiniform plexus on scrotal ultrasound (US) without a clinically palpable varicocele. Its significance remains unclear. While guidelines do not recommend surgical intervention, clinical management is variable. As there is limited information on long-term outcome of subclinical varicoceles due to challenges in diagnosis and management, we performed a single-institution, retrospective review of patients from October 1999 to October 2014 with subclinical varicocele and with available US studies reviewed by a single radiologist. Subclinical varicocele was defined as dilation of the pampiniform venous plexus on US involving > /=2 vessels with diameter > 2.5 mm, without clinical varicocele on physical examination or prior inguinal surgery. Thirty-six of 98 patients identified were confirmed as having a subclinical varicocele and analyzed. The mean age at initial visit was 15.5 years, with a mean follow-up of 26.5 months. The majority were right-sided (69.4%, n = 25), usually with a contralateral clinical varicocele. Testicular asymmetry ( > 20% volume difference of the affected side by testicular atrophy index formula) was assessed in 9 patients with unilateral subclinical varicocele without contralateral clinical or subclinical varicocele and observed in 1 patient. Of 17 patients with follow-up, 3 (17.6%) progressed to clinical varicocele without asymmetric testicular volume, as most remained subclinical or resolved without surgery. In our experience, subclinical varicoceles appeared unlikely to progress to clinical varicoceles, to affect testicular volume, or to lead to surgery. Although our study is limited in numbers and follow-up, this information may aid clinical management strategies and guide future prospective studies.