Objectives: To describe the Quality of Life (QoL) among adolescents with Patellofemoral Pain (PFP) and Osgood-Schlatter Disease (OSD) and investigate characteristics associated with QoL. Study design: Cross-sectional. Participants: 316 adolescents with PFP or OSD. Main outcome measures: QoL subscale of The Knee injury and Osteoarthritis Outcome Score (KOOS) and the EuroQol 5-dimensions (EQ-5D). Results: The KOOS-QoL was 51 ± 18, and the total index score for the EQ5D was 0.67 ± 0.21. KOOS-QoL subscale showed that 60% reported being aware of their knee problems daily or constantly, 38% reported severe to extreme lack of confidence in their knees, 28% reported severe to extreme difficulty with their knees, and 20% reported severely or totally modifying their lifestyle to avoid potentially damaging activities to their knee. EQ-5D showed that 79% experienced problems with everyday activities, 48% reported mobility problems, 17% felt worried, sad, or unhappy, and 7% reported problems looking after themselves. Conclusions: Many adolescents with longstanding non-traumatic knee pain experience low QoL. More than half were aware of their knee problems at least daily, one in three reported a severe lack of confidence in their knee, and one in six felt worried, sad, or unhappy.