OBJECTIVES: Unintended pregnancy represents a significant economic burden to the health system with an estimated medical cost for SUS of BRL4.1 billion annually. Adolescent women have a high risk of UP, mainly due to the compliance required by most of the available contraceptive methods. Therefore, as LNG-IUS effectiveness doesn’t rely on user adherence, our objective is to evaluate the budget impact of the incorporation of LNG-IUS in SUS. METHODS:  BIA was developed with a 5-year time horizon. The number of 15 to 19-year old adolescents was obtained from the Brazilian Census data (IBGE), from which 67.2% would be sexually active according to the Ministry of Health and were considered as users of contraceptive methods. Initial market share of each method was estimated from UNESCO survey. It was assumed that LNG-IUS garnered 0.7% of the contraceptive market in the first year reaching 5% in the 5^th year, taking most of its share from short-acting methods. The analysis considered the cost of each method, its medical resources and also the endpoint (UP cost). Prices of contraceptive methods were obtained from public sources: LNG-IUS 52mg (maximum government selling price) and current methods in SUS from public disclosures (Health Prices Database and the Official Gazette). Costs expressed in 2016 prices, exchange rate 1.00USD=3.70BRL. RESULTS:  The expected number of women using LNG-IUS is 279.110 after 5 years. BIA showed overall savings of BRL12.7 million in 5 years, driven mainly by decreased UP-related expenditures and long-term savings in contraceptive costs. First-year acquisition cost of the device lead to increased costs in the first 2 years of incorporation. CONCLUSIONS:  LNG-IUS is a highly effective contraceptive method that has the potential to yield savings for avoiding UP in 15 to 19-year old adolescents in the Brazilian Public Health care system.