Menstrual cups are increasingly used to control menstrual bleeding. Complication rates are sparsely described, but some serious complications have been reported. We present a rare case of ureterohydronephrosis due to a menstrual cup. A woman in her 30s presented with intermittent flank pain and occasional haematuria. CT urography showed a menstrual cup placed in the right side of the vagina in close proximity to the ureteral ostium together with ureterohydronephrosis. After removal of the menstrual cup, there was a complete regression of symptoms and ultrasonic regression of the ureterohydronephrosis. More awareness should be made, both among menstrual cup users and clinicians, about presenting symptoms and how to choose the correct shape, size, and insertion method to avoid complications.