The aim of this paper is to examine the contribution of friendship and romantic relationships on positive mental health and to explore the role of these relationships on the connection between stress and positive mental health. The purpose of this research is to examine these relationships by conceptualizing mental health as more than just the absence of psychopathology, more precisely, defining it as a concept consisting of emotional, psychological and social well-being. A total of N = 431 participants (95 males and 336 females) of younger adults participated in the study. Participants completed the Sociodemographic Data Questionnaire, Croatian version of Mental Health Continuum Short Form (Vuletić, Erdeši i Nikić, 2018), Brief Inventory of Perceived Stress (Lehman, Burns, Gagen, i Mohr, 2012), Relationship Assessment Scale (Hendrick, 1988) and Generic form of RAS (Renshaw, McKnight, Caska, Blais, 2010). The results indicate a significant contribution of friendship and romantic relationships in explaining mental health variance and the existence of a moderating effect of friendship in the relationship between mental health and stress. The participants who highly rate their friendship satisfaction, score higher results in mental health in stressful situations compared to participants who are less satisfied with friendship. Furthermore, certain gender differences were found. For male participants, in addition to stress, only romantic relationships are a significant predictor of mental health, while for women, both romantic relationships and frindship are significant predictors. Also, for men, a moderating effect of either friednship or romantic relationships was not found, while for women, a moderating effect of friendship in the relationship between stress and mental health was found. The paper describes the obtained findings, research limitations and suggestions for future research.