Background: Ovarian hyperstimulation syndrome (OHSS) is a known complication of controlled ovarian stimulation during in vitro fertilization (IVF). In severe cases, marked ovarian enlargement may lead to compression of adjacent structures. Urinary tract obstruction and subsequent pyelonephritis are rare but serious complications. Case Report: We report a woman undergoing IVF who developed severe OHSS and presented with fever, abdominal distension, and flank pain. Imaging revealed enlarged ovaries causing ureteric compression with resulting hydronephrosis and obstructive pyelonephritis. The patient was treated with intravenous antibiotics and supportive management, leading to clinical improvement. Conclusion: Obstructive pyelonephritis secondary to OHSS is an uncommon complication. Early recognition and prompt management are essential to prevent serious renal and systemic complications.