Introduction: Rugby union has one of the highest injury incidence rates among all collective sports. Data on incidence and type of injuries at non-professional level in rugby are sparse. Our objective was to assess the severity, incidence, type and location of injuries sustained during the top-tier of the Portuguese rugby union senior male fifteens championship. Methods: A cohort prospective study recording time-loss injuries occurring during the 2017/18 season in Portugal was conducted. All senior male top-tier clubs were invited to participate. Main outcome measures included: incidence rate, anatomical location, type, injury incident and severity. Data were collected using an online platform. Methodology used was similar to previously published studies, and Ethical approval was obtained. Results: A total of 91 injuries were recorded corresponding to an overall incidence rate of 37.92 injuries per 1000 player match-hours. Average severity was 28.16 days. Contact preceded 84.6% of injuries, and tackle was responsible for 48.1%. Most injuries occurred in the lower limb (50.5%) and were joint/ligament or muscle/tendon injuries (31.9 and 20.9%, respectively). Incidence rate was lower at club level in fifteens, when compared to Portuguese rugby sevens or international fifteens. However, injury severity did not differ from previous studies. Conclusions: Injury incidence was lower in the Portuguese club competition, compared to other studies in elite international and Portuguese sevens studies, being similar to other community level and non-elite studies in rugby. During a match in the top Portuguese rugby championship, an average of 1.52 injuries may occur, leading to an average absence of 4 weeks. This represents a significant burden to players and teams and strategies aiming at its mitigation should continue to be considered and designed.