Little is known about the epidemiology of widespread pain (WSP) in children and adolescents. This study aims to estimate the new-onset and prognosis of WSP in schoolchildren and investigate factors predicting its development. A prospective study was conducted among 1756 schoolchildren (age 10-12 years) in Southern Finland. At baseline, information was collected on WSP, regional musculoskeletal pain symptoms, depressiveness, fatigue, sleep problems, physical activity and joint hypermobility. These children were contacted again 1 year and 4 years later to determine the outcome and the new-onset of WSP. A total of 1282 children (73%) of the baseline study population were found at both follow-ups. Of the children who had WSP at baseline, 31% and 30% reported persistence/recurrence of symptoms at 1- and 4-year follow-up, respectively. However, only 10% of these children reported WSP at both 1 and 4 years. Of the children who were free of WSP at baseline, 18% reported new-onset WSP at 1-year follow-up and 3% reported these symptoms at both follow-up times. The independent baseline risk factors of WSP were older age (OR 1.3 95% CI 1.0-1.8), female gender (OR 1.4, 1.1-1.9), depressiveness (OR 1.5, 1.1-2.2) and regional back pain symptoms (Neck pain: OR 1.7, 1.1-2.4; Upper back pain: OR 2.1, 1.1-4.1; Lower back pain: OR 3.0, 1.6-5.7). Both psychological factors and somatic pain symptoms predict future development of WSP in adolescents.