This study focused on the direct and indirect effect (via sleep duration) of computer use on psychological and somatic symptoms among boys and girls (N = 6112) in 3 different age cohorts (11, 13, and 15-years old) from the 2013/2014 health behaviour in school-aged children (HBSC) study done in Sweden. Structural equation modeling (with SPSS AMOS 22) was used (specifying separate multigroup models for each age group). The mediating effect of sleep duration was tested for significance using a Bootstrap estimation. Across the age groups, the direct effect of computer use was found to be a significant risk factor for psychological and somatic symptoms among both girls and boys (all the P values < 0.05), as the associations between computer use was only partly mediated by sleep duration. Additionally, the magnitude of the effects for the association between computer use and both psychological and somatic symptoms was quite similar among boys and girls across different age cohorts, but tended to be more pronounced among 13-year old girls. In particular, the direct and indirect effect computer use on psychological symptoms was significantly stronger among girls in this age cohort (all the P values < 0.05). Even though the cross-sectional design of the study prevented causal conclusions, the development of strategies to reduce children and adolescents’ computer screen time and the need to focus on mechanisms relating ICT use to somatic and psychological symptoms were emphasized.