The gold standard for the diagnosis of pelvic congestion syndrome (PCS) is venography (VG), although transvaginal ultrasound (TVU) might be a noninvasive, nonionizing alternative. Our aim is to determine whether TVU is an accurate and comparable diagnostic tool for PCS. An observational prospective study including 67 patients was carried out. A TVU was performed on patients, measuring pelvic venous vessels parameters. Subsequentially, a VG was performed, and results were compared for the test calibration of TVU. Out of the 67 patients included, only 51 completed the study and were distributed in two groups according to VG results: 39 patients belonging to the PCS group and 12 to the normal group. PCS patients had a larger venous plexus diameter (15.1 mm vs. 12 mm; p = 0.009) and higher rates of crossing veins in the myometrium (74.35% vs. 33.3%; p = 0.009), reverse or altered flow during Valsalva (58.9% vs. 25%; p = 0.04), and largest pelvic vein ≥ 8 mm (92.3% vs. 25%). The sensitivity and specificity of TVU were 92.3% (95% CI: 78.03–97.99%) and 75% (95% CI: 42.84–93.31%), respectively. In conclusion, transvaginal ultrasonography, with the described methodology, appears to be a promising tool for the diagnosis of PCS, with acceptable sensitivity and specificity.