This study examines the social determinants of psychosomatic complaints in young adolescents. Using data from the Health Behaviour in School-aged Children (HBSC) study, psychosomatic complaints are studied in 98,773 adolescents (11- and 13-year-olds; 48% 11-year-olds, 52% 13-year-olds; 52% females, 48% males) from 34 European countries. Individual-level determinants, including family-, peer- and school-related factors as well as country-level determinants (Human Development Index [HDI]) are considered. In line with existing evidence, results revealed more psychosomatic complaints in young adolescents experiencing stress inducing familial-, peer- and school-related factors. Negative effects of poor friendships, negative class climate, school pressure, and high media use were more pronounced for girls. After controlling for these factors, a higher HDI was related to a lower risk for psychosomatic complaints. Gender-specific intervention programs should aim at improving the quality of relationships, especially among peers, to prevent psychosomatic complaints among young adolescents.