INTRODUCTION: Mental health inequalities are an increasingly important global problem. This study examined the association between mental health status and certain socioeconomic indicators (personal social position and the socioeconomic status of the family) in Slovenian 15-year-old adolescents. METHODS: Data originate from the WHO-Collaborative cross-national ‘Health Behavior in School-aged Children’ study conducted in Slovenia in 2010 (1,815 secondary school pupils, aged 15). Mental health status was measured by: KIDSCREEN-10, the Strength and Difficulties questionnaire (SDQ), a life satisfaction scale, and one question about feelings of depression. Socioeconomic position was measured by the socioeconomic status of the family (Family Affluence Scale, perceived material welfare, family type, occupational status of parents) and personal social position (number of friends and the type of school). Logistic regression and a multivariate analysis of variance (MANOVA) were performed. RESULTS: Girls had 2.5-times higher odds of suffering feelings of depression (p < 0.001), 1.5-times higher odds of low life satisfaction (p = 0.008), and a greater chance of a lower quality of life and a higher SDQ score than boys (p = 0.001). The adolescents who perceived their family's material welfare as worse had 4-times higher odds (p < 0.001) of a low life satisfaction, a greater chance of a low quality of life, and a higher SDQ score than those who perceived it as better (p < 0.001). Adolescents with no friends had lower KIDSCREEN-10 and higher SDQ scores than those who had more than three friends. CONCLUSIONS: Despite the fact that Slovenia is among the EU members with the lowest rates of social inequalities, it was found that adolescents with a lower socioeconomic position have poorer mental health than those with a higher socioeconomic position. Because of the financial crisis, we can expect an increase in social inequalities and a greater impact on adolescents' mental health status in Slovenia in the future.