Introduction: Swimming and water polo belong to different groups when their structural complexity of kinesiological activity is observed. What they have in common is the water medium, the specificity of movements in the shoulder joint and shoulder girdle and the constant raising of the arms above the head, which is why shoulder injuries often occur in both sports as a result of a combination of different factors. Aim of the research: This research primarily aims to show a comparison of the frequency of shoulder joint injuries in two sports, swimming and water polo. Furthermore, specific objectives include investigating the relationship of the following variables to the incidence of shoulder injuries: 1) number of workouts in the water and in the gym/exercise hall; 2) number of hours of training in the water and in the gym/exercise hall; 3) conducting exercises for injury prevention; 4) performing stretching and going to massages. Respondents and methods: The total number of respondents who participated in the study was 36, of which 20 were male and female swimmers and 16 were water polo players. The research was conducted during April, May and June 2022 in swimming and water polo clubs throughout Croatia. A non-standardized 15-question online survey questionnaire developed in Microsoft Forms was used for the purposes of this research. Descriptive statistics included the calculation of the arithmetic mean, standard deviation, standard error, and range of results. The parametric Student's test (the t-test) for independent small samples, was used to test the hypotheses, and the statistical significance was presented as P > 0.05 (5%). Results: The Student 's test revealed the absence of a statistically significant difference between swimmers and water polo players in the frequency of shoulder joint injuries. There was also no statistically significant difference in the incidence of shoulder joint injuries between groups in terms of the number of water and gym/exercise hall workouts, the number of water and gym/exercise hall workout hours, and stretching and massage. A statistically significant difference was shown when examining the association between the frequency of shoulder joint injury and performing exercises for injury prevention. Conclusion: There is a need for further study and research on the frequency of shoulder injury in swimmers and water polo players as well as the mechanism of shoulder injury in order to better understand the principle of injury with other factors such as number and hours of training, prevention and stretching, going to massages and more.