Retroperitoneal leiomyomata are infrequent, and their prevalence among primary retroperitoneal tumours has been estimated as 0.5-1.2%. The authors report a case of symptomatic retroperitoneal leiomyoma with a favourable prognosis. A 53-year-old woman presented for abdominal pain associated to an inflammatory syndrome. A contrast-enhanced computed tomography revealed a large abdominopelvic mass and patient underwent open surgical excision. Definitive diagnosis was done after immunohistochemical assessment. Immunoreactivity was strong for smooth muscular actin. Presence of oestrogen and progesterone receptor proteins was also detected. Prognosis of these well-differentiated smooth muscle tumours is generally favourable but a postoperative surveillance is always recommended.