This study examined associations between loneliness, a construct associated with serious adverse mental health outcomes, and positive mental wellbeing. Validated measures of loneliness (represented by friendship-related loneliness, isolation, positive attitude to solitude, and negative attitude to solitude) and positive mental wellbeing were administered to 1,143 adolescents from urban and rural schools. Confirmatory factor analyses revealed satisfactory model fit for both measures. A structural equation model confirmed significant positive associations between positive mental wellbeing and friendship-related loneliness and positive attitude to solitude; a significant negative association was found for isolation. Regression analyses provided support for significant differences in these associations according to gender, age, and geographical location (although only marginally). The implications of these findings during adolescence are reviewed.