Low back pain (LBP) is common among adolescents and it has been estimated that one-fifth of adolescents suffer from recurrent severe LBP. However, longitudinal studies describing the risk factors of LBP are scarce. The purpose of this study was to investigate whether health, physical activity and other health behaviors, socio-demographic background and school success predict LBP hospitalization until early middle age. A cohort of 72,378 adolescents (57,408 respondents, response rate 79%) aged 14-18 years participating in a population survey between 1979 and 1997 was followed for an average of 11.1 years through the national hospital discharge register. We identified 810 (1.1%) persons with LBP hospitalization, 620 males (1.7% of the whole male cohort) and 190 (0.5%) females (HR 3.2; 95% CI: 2.7-3.7). In multivariate Cox's analysis, the strongest risk factors for LBP hospitalization for the whole cohort were weekly health complaints (HR 1.5; 95% CI: 1.2-1.9), daily smoking (HR 1.4; 95% CI: 1.1-1.7), and poor school success (HR 1.4; 95% CI: 1.1-1.9). Late puberty decreased the risk in males (HR 0.7; 95% CI: 0.5-0.9). Among females, participation in organized sports (HR 1.7; 95% CI: 1.1-2.5) was associated with an increased risk for LBP hospitalization. The associations between the risk factors and LBP hospitalization persisted into adulthood. Efforts to reduce adolescent smoking may decrease LBP-related morbidity in males. Coaches should pay special attention to the nature of physical training and personal exercises in females, and physiotherapists and sports physicians to the prevention of LBP hospitalization.