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Objectives: Numerous risk factors have been identified for patellar tendinopathy (PT), often in small population studies. The aim was to use an international online questionnaire to generate a large database and identify significant risk factors. Design: Case-control study. Setting: Private practice and sporting teams recruited from England, Spain, and Italy with the questionnaire available in all 3 languages (equivalence between online and self-administration shown previously). All data were anonymized and password protected. Participants: Eight hundred twenty-five data sets collected between January 2012 and May 2014. Assessment of Risk Factors: A total of 23.4% of participants had clinically diagnosed PT. A comparison between these participants and participants without PT was made. Main outcome measure: Association between the presence of PT and risk factors. Results: Eight risk factors were included in the analysis based on a purposeful selection procedure: sex, hours of training, hamstring flexibility, previous patellar tendon rupture, previous knee injury, current/previous back pain, family history, and age. Four were found to have statistically significant odds ratios: female sex [0.70, 95% confidence interval (CI), 0.49-1.00, P = 0.05], hours of training (>20 hours 8.94, 95% CI, 4.68-17.08, P < 0.01), previous knee injury (2.10, 95% CI, 1.45-3.04, P < 0.01), and flexible hamstrings (0.61, 95% CI, 0.38-0.97, P = 0.04). There was a trend toward association for back pain (1.45, 95% CI, 0.99-2.14, P = 0.06) and a family history of tendon problems (1.51, 95% CI, 0.96-2.37, P = 0.08). Conclusions: Risk factors have been identified that are potentially modifiable to inform prevention and rehabilitation programs; future research is required to establish causal relationships. Identified risk factors require mechanistic investigation as they are not currently recognized in the literature. [ABSTRACT FROM AUTHOR]