Levonorgestrel releasing-intrauterine systems (LNG-IUS) were originally developed as a method of contraception in the mid 1970s. The only LNG-IUS approved for general public use is the Mirena LNG-IUS, which releases 20 mcg of levonorgestrel per day directly in to the uterine cavity. However, new lower dose (10 and 14 mcg per day) and smaller sized LNG-IUS (MLS, FibroPlant-LNG) are currently under clinical development and investigation. Research into the non-contraceptive uses of LNG-IUS is rapidly expanding. In the UK, LNG-IUS is licensed for use in menorrhagia and to provide endometrial protection to perimenopausal and postmenopausal women on estrogen replacement therapy. There is limited evidence to suggest that LNG-IUS may also be beneficial in women with endometriosis, adenomyosis, fibroids, endometrial hyperplasia and early stage endometrial cancer (where the patient is deemed unfit for primary surgical therapy). This systematic enquiry and overview evaluates the quality of evidence relating to the non-contraceptive therapeutic uses of LNG-IUS in gynaecology.