BACKGROUND:The prevalence of adolescent knee pain is 33%, and patellofemoral pain (PFP) is the most common diagnosis with a nontraumatic onset. The 2-year prognosis of adolescent PFP compared with other types of knee pain is unknown. PURPOSE:To investigate the 2-year prognosis of knee pain among adolescents with and without a diagnosis of PFP. STUDY DESIGN:Cohort study; Level of evidence, 2. METHODS:In 2011, a cohort of 2200 adolescents aged 15 to 19 years answered an online questionnaire on musculoskeletal pain. Of these, 504 reported knee pain, and 153 of these were clinically diagnosed with PFP. After 2 years, the 504 adolescents, as well as 252 randomly selected adolescents who did not report knee pain in 2011, were contacted again. Primary outcome at follow-up was the proportion of adolescents with knee pain during the last week prior to follow-up. RESULTS:Overall, 55.9% (95% CI, 50.8%-60.9%) of those reporting knee pain at baseline also reported pain 2 years later. Adolescents diagnosed with PFP had a 1.26 (95% CI, 1.05-1.50) higher relative risk (RR) of knee pain at follow-up compared with other types of knee pain. Adolescents with PFP were significantly more likely to reduce or stop sports participation compared with adolescents with other types of knee pain. Of those without knee pain at baseline, 12.8% (95% CI, 8.4%-17.2%) reported knee pain at follow-up in 2013. Adolescents with knee pain at baseline had a 4.51 (95% CI, 3.15-6.45) higher RR of knee pain at follow-up compared with adolescents without knee pain at baseline. CONCLUSION:Knee pain during adolescence, and PFP in particular, is in most cases present after 2 years and thus may not be self-limiting. A greater focus on early detection and prevention of knee pain during adolescence is needed.