Problem: Epidemiological data of injuries and illnesses in water polo athletes are limited. This studys objective was to describe the incidence, prevalence, and severity of health problems among a cohort of elite Players.Methods: We conducted a prospective cohort study with 24 elite waterpolo athletes over 2.5 years. Health problems were recorded weekly with the Oslo Sports Trauma Research Center Questionnaire on health problems and subsequently categorized into illnesses and injuries according to the recently published International Olympic Committee guidelines. Based on the athletes weekly responses, we calculated health problem prevalence, incidence and severity.Results: A total of 288 health problems were reported, including 76 illnesses and 212 injuries resulting in a weekly prevalence of 30.3% (95% CI: 28.2-32.4) for all health problems. Of these, 115 (39.9%) were categorized as substantial, of which 76 were illnesses, and 39 were injuries. The overall acute injury incidence rate was 1.66 injuries (95% CI: 1.23-2.09) per 1,000 sports exposure hours. The training and competition acute injury incidence rates were, respectively, 1.20 (95%CI: 0.81 1.59) per 1,000 training hours and 5.38 (95% CI: 3.18 7.58) per 1,000 competition hours.Conclusion: There was a high prevalence of injuries among this cohort of elite water polo athletes. Future efforts that further improve athlete safety should focus on both acute and repetitive mechanism injuries.Key Words: Epidemiology, Acute Injury, Repetitive Injury, Injury Mechanism