Obturator hernia of the ureter is uncommon. Computed tomography of a 77-year-old woman with sudden-onset lower left abdominal pain and urinary symptoms showed an obturator hernia with ureteral entrapment. Obturator hernia is a diagnostic challenge because the hernial mass is very insidious. It should be suspected in emaciated, multiparous, elderly women presenting with unexplained pain in the groin, hip, thigh or knee. High levels of clinical suspicion of high-risk patients and recourse to investigation by computed tomography are important, as delay in diagnosis and treatment is associated with increased morbidity and mortality.