Intrauterine device is a popular, cost-effective method of contraception known worldwide. It is extremely effective, with pregnancy rates comparable to tubal ligation (5-year cumulative rate varying from 0.5 to 1.1). LNG-IUS increases in popularity and may be used as the method of choice for adults because it offers non-contraceptive benefits: slight menstrual bleeding, decreased number of incidents of dysmenorrhea, and reduced pain associated with endometriosis. The levonorgestrel-releasing intrauterine system (LNG-IUS) provides a release rate of 20 mu g/24h of levonorgestrel. The hormone released from the intrauterine device causes some systemic changes, however local effects, such as glandular atrophy and stromal decidualization, in addition to foreign body reaction, are dominant. According to the Food and Drug Administration regulations, category X was assigned to LNG. The use of the product is contraindicated in women who are or may become pregnant. We report a case of a 30-year old woman who has already been pregnant before the insertion of a levonorgestrel -releasing intrauterine system (LNG-IUS). The patient was lactating after the previous pregnancy the first menstruation had not appeared yet.