Poor Mental health in adolescence has become more prevalent over the past decades. Differences between gender and age in mental health are apparent where girls rate their mental health lower than boys. Socioeconomic status has proven to be a determinant for poor mental health, however in detecting poor mental health, the use of solely objective measures may not suffice. The aim of this cross-sectional study was to explore different aspects of socioeconomic status and their association with school children’s mental health. The data was obtained from the 2009/10 HBSC survey in Sweden. A sample of 4449 students aged 11 and 15 was included. Binary logistic regression with odds ratio (OR) and 95% confidence intervals (95%CI) was used to estimate the associations between the different aspects of SES and mental health outcomes. The relationship between poor mental health and low subjective economic status was significant while no such relationship was found in the other SES-measures. The use of subjective economic status may be a more reliable determinant for poor mental health than objective and relative measures. Future studies should focus on developing targeted interventions, also on the understanding of socioeconomic status in childhood.