Contemporary research in psychology is oriented towards promotion of positive youth development (PYD) (Larson, 2006). Lerner's framework (2005) identifies five characteristics to measure PYD: caring, competence, connection, character and confidence. Relationships with caring adults are a part of adolescents' social context that can enhance these characteristics (Bowers et al., 2014). The goal of this research was to describe the nature of relationships adolescents have with important adults and to examine the characteristics of these relationships and how they contribute to PYD. Participants were 277 high school students, who completed Inventory of positive youth development (Arnold, Nott & Meinhold, 2012), Inventory of socially supportive behaviours (Barrera, 1981), Closeness scale for relationships with important adults and questions about other characteristics of important adults and adolescent's relationship with them. Contexts of these relationships were examined with open-ended questions. The result showed that the majority of adolescents have an important adult in their life and value them highly. Important adults are mostly of the same gender as adolescents, related to them and deemed as role models. They help adolescents to achieve higher well-being through three processes proposed by Rhodes (2005): through social and emotional development, identity development and cognitive development. Adolescents know their important adults on average for more than ten years, they see them and receive support from them at least once a week and they usually do not have conflicts with them. The high quality of these relationships is evident from high levels of closeness and satisfaction in relationships. There are no differences in the majority of these characteristics between boys and girls. Significant predictors of PYD characteristics are the gender of adolescents, education level of important adults, mutuality, the frequency of conflict and the satisfaction with relationship.