Background <p>Testicular vein syndrome is a rare and under-recognized cause of ureteral obstruction due to extrinsic compression by a dilated or tortuous testicular vein. With fewer than 20 cases reported in the literature, it often presents with nonspecific symptoms, and no standardized diagnostic criteria currently exist.</p> Case presentation <p>We report the case of a 35-year-old Arab male with a 2-year history of intermittent left flank pain without urinary symptoms or nephrolithiasis. Imaging studies revealed left-sided hydronephrosis with no calculi. Contrast-enhanced computed tomography in the excretory phase demonstrated a mildly dilated left testicular vein crossing anterior to the proximal ureter, causing proximal ureteral and renal pelvic dilation. Scrotal Doppler ultrasound confirmed ipsilateral testicular varices. Notably, the patient experienced increased flank pain during the Valsalva maneuver, a finding we term the “Valsalva Flank Pain Sign.”</p> Conclusions <p>This case highlights the diagnostic challenges of testicular vein syndrome and underscores the importance of detailed imaging and clinical correlation. The proposed Valsalva Flank Pain Sign may serve as a simple bedside tool to raise suspicion of this rare entity. Excretory-phase computed tomography remains the imaging modality of choice for diagnosis. The association with testicular varices suggests a potential shared pathophysiological mechanism involving venous hypertension.</p>