Objective The aim of the present study was to identify variables associated with treatment failure in women with menorrhagia who were treated with thermal balloon ablation (TBA) or levonorgestrel releasing intrauterine system (LNG-IUS), and to determine if there are subgroups where one treatment type is more effective than the other. Methods The study included 106 women with menorrhagia who were treated with TBA or LNG-IUS at the study institute between January 2003 and December 2007, with a follow-up period greater than 12 months. Data were collected by retrospective review of medical records. Treatment failure was defined as persistent or recurrent menorrhagia within one year after treatment or hysterectomy at any time during follow-up. The relationships between variables and treatment outcome were analyzed using the chi-square or Fisher`s exact test. The treatment outcome of TBA was compared with LNG-IUS. Results Sixty-seven women were treated with TBA and 39 women were managed with LNG-IUS. Fifty-two women had a myoma ≥2.5 cm. Treatment failure was observed in 24 women (2 recurrent or persistent menorrhagia and 22 hysterectomies) and myoma size (≥2.5 cm vs. <2.5 cm) was associated with treatment outcome. TBA and LNG-IUS showed similar treatment outcomes. Conclusion A large myoma is a risk factor for treatment failure in women with menorrhagia treated with TBA or LNG-IUS.