The incorrect carriage of schoolbags and heavy bags may result in back pain (BP) in adolescents. Our objective was to assess the problem of BP and associated factors among adolescents. This was a cross-sectional study targeting intermediate and secondary school adolescents in Abha City, Saudi Arabia. An anonymous questionnaire for BP was used. Student body weight and the weight of their full schoolbag were measured. The study included 876 adolescents. An overall prevalence of BP of 39.4% (95% CI: 35.3-43.7) was found. Upper BP (UBP), middle BP (MBP), and lower BP (LBP) amounted to 14.5%, 13.4%, and 11.5%, respectively. Associated significant factors with MBP were carrying the bag on one side compared to on the back (adjusted odds ratio (aOR) = 2.13, 95% CI: 1.20-3.73) and being at intermediate level compared to secondary (aOR = 1.56, 95% CI: 1.04-2.40). On the other hand, gender and schoolbag weight/body weight percent were not found to be significantly associated with MBP. None of the studied factors were significantly associated with overall BP, UBP, or LBP. BP is a prevalent among adolescents in southwest Saudi Arabia. One-sided schoolbag carriage is a significant associated factor for middle back pain. Parents and teachers should encourage students to consider the correct way to carry schoolbag.