Pelvic organ prolapse (POP) is not regarded as life-threatening, and has been left undiagnosed on occasion. However, in some cases, the condition has resulted in hydronephrosis and renal failure. We have investigated the prevalence of hydronephrosis in patients with POP at the Female Pelvic Floor Medicine Center, and how it may be improved through surgery. Of the 555 patients examined between January 2016 and December 2017, 265 patients were diagnosed with POP. This study involved 192 of these cases diagnosed with POP as subjects. Using preoperative ultrasound scanning, hydronephrosis was classified into four categories depending on severity. At the time of surgery, the conditions of POP were classified into stages I to IV of the POP Quantification (POP-Q) system. Of these 192 patients, 20 (10.4%) had been evaluated as hydronephrosis (slight hydronephrosis 9, mild hydronephrosis 6, and severe hydronephrosis 5). It is known that as the staging of POP progresses, the likelihood of developing hydronephrosis also increases. In 20 cases with POP-Q stage IV, 7 were confirmed to have hydronephrosis; 3 of these were severe hydronephrosis. The 6 cases of mild, and 5 cases of severe hydronephrosis achieved cure after tension-free vaginal mesh TVM surgery. POP may cause hydronephrosis, so examination of the upper urinary tract is necessary. Ultrasound scans are useful in detecting hydronephrosis. There has been a case where it took 6 to 10 months for hydronephrosis to improve, so early diagnosis and management are crucial in order to prevent hydronephrosis. TVM surgery can be used for repair of not only anterior prolapse, but also uterine prolapse, which can be thus treated without hysterectomy, and this has the potential to improve hydronephrosis.