Report eccentric knee flexor strength values of elite Gaelic football players from underage to adult level whilst examining the influence of body mass and previous hamstring injury.Cross-sectional study.Team's training facility.Elite Gaelic football players (n = 341) from under 14 years to senior age-grades were recruited from twelve teams.Absolute (N) and relative (N·kg-1) eccentric hamstring strength as well as corresponding between-limb imbalances (%) were calculated for all players.Mean maximum force was 329.4N (95% CI 319.5-340.2) per limb. No statistically significant differences were observed in relative force values (4.4 N ·kg-1, 95% CI 4.2-4.5) between age-groups. Body mass had moderate-to-large and weak associations with maximum force in youth (r = 0.597) and adult (r =0 .159) players, respectively. Overall 40% (95 CI 31.4-48.7) presented with a maximum strength between-limb imbalance >10%. Players with a hamstring injury had greater relative maximum force (9.3%, 95% CI 7.0-11.8; p > 0.05) and a 28% (95% CI 10.0-38.0) higher prevalence of between-limb imbalances ≥15% compared to their uninjured counterparts.Overlapping strength profiles across age-groups, combined with greater strength in previously injured players, suggests difficulties for establishing cut-off thresholds associated with hamstring injury risk.