Mental health and problematic use of the Internet are relatively new constructs, and researchers are examining a number of factors that contribute to them. The aim of this study was to examine the relationship between mental health defined as emotional, psychological and social well-being, problematic internet use, problems in emotional regulation and loneliness in young people. Also, the aim of the research was to investigate the contribution of emotional regulation and loneliness in explaining the problematic use of the Internet, as well as the contribution of these variables in explaining mental health. The research was conducted online and 395 respondents (257 women and 138 men), aged 15 to 35 years (M = 21.08, SD = 5.04) participated in the research. The results of the correlation analyzes show a significant connection between mental health, problematic use of the Internet, difficulties in emotional regulation and loneliness. Gender differences in these constructs were also checked, and it was found that women showed significantly more problematic use of the Internet and greater difficulties in emotional regulation compared to men. Furthermore, four hierarchical regression analyzes were conducted to examine problematic Internet use and mental health. The first hierarchical regression was conducted in such a way that loneliness and difficulties in emotional regulation were predictors of problematic Internet use. It has been shown that respondents who have more difficulties in emotional regulation and who are more lonely have a greater tendency for problematic use of the Internet. The remaining three hierarchical regression analyzes examined the contribution of predictors of loneliness, difficulties in emotional regulation, and problematic Internet use in explaining mental health criteria (emotional, psychological, and social well-being). Analysis of the results shows that respondents with greater difficulties in emotional regulation, those who are more lonely and who prefer online contact, show lower emotional and psychological well-being, while respondents who are lonely and who have more difficulties in emotional regulation show reduced social well-being. The results suggest the importance of emotional regulation and loneliness in predicting problematic Internet use and mental health.