Background: Hamstring injury is one of the most common injuries affecting gaelic footballers, similar to other field sports. Research in other sports on whether residual hamstring weakness is present after hamstring injury is inconsistent, and no study has examined this factor in irish gaelic footballers. The aim of this study was to examine whether significant knee muscle weakness is present in male Irish gaelic footballers who have returned to full activity after hamstring injury. Methods: The concentric isokinetic knee flexion and extension strength of 44 members of a university gaelic football team was assessed at 60, 180 and 300 degrees per second using a Contrex dynamometer. Results: Fifteen players ( 34%) reported a history of hamstring strain, with 68% of injuries affecting the dominant ( kicking) limb. The hamstrings were significantly stronger ( p < 0.05) on the dominant limb in all uninjured subjects. The previously injured limbs had a significantly lower ( p < 0.05) hamstrings to quadriceps ( HQ) strength ratio than all other non-injured limbs, but neither their hamstrings nor quadriceps were significantly weaker ( p > 0.05) using this comparison. The previously unilaterally injured hamstrings were significantly weaker ( p < 0.05) than uninjured limbs however, when matched for dominance. The hamstring to opposite hamstring ( H: oppH) strength ratio of the previously injured players was also found to be significantly lower ( p < 0.05) than that of the uninjured players. Conclusion: Hamstring muscle weakness was observed in male Irish gaelic footballers with a history of hamstring injury. This weakness is most evident when comparisons are made to multiple control populations, both within and between subjects. The increased strength of the dominant limb should be considered as a potential confounding variable in future trials. The study design does not allow interpretation of whether these changes in strength were present before or after injury.