BACKGROUND: Epidemiological data on sports injuries and illnesses depend on the surveillance methodology and the definition of the health problems. The effect of different surveillance methods on the data collection has been investigated for overuse injuries, but not for other health problems such as traumatic injuries and illnesses. PURPOSE: The purpose of this study was to investigate the new surveillance method developed by the Oslo Sports Trauma Research Center (OSTRC), which is based on any complaint definition (new method), to identify health problems compared with the traditional surveillance method, which is based on time loss definition. STUDY DESIGN: Descriptive epidemiology study. METHODS: A total of 62 Japanese athletes were prospectively followed-up for 18 weeks to assess differences in health problems identified by both new and traditional methods. Every week, the athletes completed the Japanese version of the OSTRC questionnaire (OSTRC-H2.​JP), whereas the teams' athletic trainers registered health problems with a time loss definition. The numbers of health problems identified via each surveillance method were calculated and compared with each other to assess any differences between their results. RESULTS: The average weekly response rate to the OSTRC-H2.​JP was 82.1% (95% CI, 79.8-84.3). This new method recorded 3.1 times more health problems (3.1 times more injuries and 2.8 times more illnesses) than the traditional method. The difference between both surveillance methods' counts was greater for overuse injuries (5.3 times) than for traumatic injuries (2.5 times). CONCLUSIONS: This study found that the new method captured more than three times as many health problems as the traditional method. In particular, the difference between both methods' counts was greater for overuse injuries than for traumatic injuries. LEVEL OF EVIDENCE: 2b.