Purpose: To determine the prevalence of isolated right-sided varicocele due to an obstructing malignancy in patients with no other evidence of malignancy. Methods: This retrospective, multi-institutional study included a text search for right-sided varicocele in consecutive reports of scrotal ultrasound studies performed between 4/22/1999 and 06/24/2018. Diagnosis was confirmed by a radiologist based on the following criteria: pampiniform plexus vein diameter of ≥ 2 mm, which has augmented flow or increases by ≥ 1 mm on Valsalva. Inclusion criteria for adequate follow-up were (1) abdominopelvic CT or MRI performed within 3 months prior to, or any time after, the ultrasound study; or (2) presence of clinical documentation more than 2 years after the ultrasound date. Exclusion criteria were existing cancer diagnosis in the abdomen or pelvis, epididymo-orchitis, intratesticular or intrascrotal mass, and prior scrotal surgery. Images of available CT or MRI studies were reviewed for presence of any explanation of right-sided varicocele. Results: 210 patients with right-sided varicocele met inclusion and exclusion criteria. 118/210 had abdominopelvic CT or MRI in the assigned timeframe. Of these, no patients had malignancy that could account for right-sided varicoceles. Of the 92/210 patients without CT or MRI but with available clinical follow-up, none had a malignancy that could have caused an isolated right-sided varicocele. There was no underlying malignancy to explain the right-sided varicocele in any of the patients, 0/210, 95% CI [0.0–1.4%]. Conclusion: No associated malignancy was found in patients with isolated right-sided varicoceles to support additional imaging for malignancy screening.