Objective: We investigated the correlation of acute flank pain incidence with the number of pregnancies and hydronephrosis. Materials and Methods: Forty-eight patients were included in the study. Patients with urinary tract infection, abnormal urinalysis and urinary stone have been excluded. Twenty-four patients were nulliparous, and the remainder multiparous. All patients underwent urinary ultrasound by the same radiologist. The visual analog scale (VAS) was completed at the time of admission. Intravenous fluid, paracetamol and oral nitrofurantoin were administered to all patients. Patients who did not benefit from conservative treatment underwent ureteral JJ stent placement. Results: Nulliparous pregnant were younger and had earlier gestational weeks (25.1±3.7 - 28.7±3.8 p=0.004 and 22.9±3.7 - 26.3±4.0 p=0.005), as well as higher VAS scores. In nulliparous pregnant women, a significant, medium level-positive correlation was found between the degree of hydronephrosis (DoH) and the VAS scores. We observed that the higher DoH was related to higher VAS scores. However, in multiparous pregnant women, no correlation was observed between DoH and VAS scores. In the comparison of two groups, there were no significant differences in body mass index, DoH, hydronephrosis side, serum creatinine levels, type and side of pain. Forty-two percent of the patients described colic pain. Fortyfour patients benefitted from conservative treatment, whereas only 4 patients underwent JJ stent insertion. Conclusion: This study demonstrates the correlation between acute flank pain and hydronephrosis. The DoH increases as the pain intensifies, especially in the nulliparous, where the correlation is stronger