We report a rare case of endometriosis of the groin in a young woman. This case shows how difficult the diagnosis of unusual manifestations of endometriosis can be. The diagnosis was suspected by a careful history and physical examination. Diagnosis was supported by timely performed Magnetic Resonance Imaging, which illustrates its additional value. It can be argued that MRI could be the first choice of imaging technique for the assessment of young women with nonspecific or unexplained complaints of the groin. Even more important is the familiarity of physicians other than gynaecologists with rare manifestations of this common disease.