The development of the high performance athlete involves cyclical periods of training and competition. Accurate and precise measurement of body composition forms a central role in the development of the athlete or team yet longitudinal change in body composition is rarely reported. In this study we report the longitudinal change in body composition of elite, inter-county hurlers within season and over four sequential seasons. Whole body and segmental body compositional analysis was measured by dual energy x-ray absorptiometry (DXA) on 66 senior, male, outfield, inter-county hurlers, mean age 23.7 [95% CI, 22.9 : 24.5] y in the off-season period in September (BASAL). Further measurements were obtained at approximately 3 month intervals pre-competition (PRE), within-competition (IN) and in the off-season (OFF) of the following year. In addition, 11 players were followed across four consecutive seasons. Data are reported as the mean [95% CI]. Repeated measures ANOVA was used to assess change over time. Statistical significance was detected at 0.05 α-level. Estimates of effect size were calculated separately, η2 pertains to change over time while R2 is used to represent the effect between composite variables and constituents, i.e. Δ fat mass and Δ body mass. No change for body mass was observed from BASAL to PRE (0.21 kg [-0.77 : 0.39], -0.2% [-0.8 : 0.4], p = 1.000, η2 = 0.007). A moderate reduction in body mass occurred from PRE to IN (-0.78 kg [-1.21 : -0.35], -0.9% [-1.4 : -0.4], p = 0.002, η2 = 0.169) but increased from IN to OFF (1.46 kg [0.98 : 1.94], 1.7% [1.2 : 2.3], p < 0.001, η2 = 0.369). No change was observed between BASAL and OFF (0.47 kg [-0.09 : 1.04], 0.61% [-0.06 : 1.28], p = 0.219, η2 = 0.049). A concurrent increase in lean mass (1.04 kg [0.64 : 1.43], equivalent to 1.6% [1.0 : 2.2], p < 0.001, η2 = 0.307), and decrease in fat mass (-1.26 kg [-1.64 : -0.87] equivalent to -8.1% [-10.8 : -5.5], p < 0.001, η2 = 0.365), was observed BASAL to PRE. This was followed by the restoration of fat mass in the period IN to OFF (1.73 kg [1.33 : 2.12] or 12.4% [9.5 : 15.7], p < 0.001, η2 = 0.54 ), with the trunk acting as the primary region of change (1.07 kg [0.84 : 1.30], R2 = 0.93). Longitutinally, over four years, an overall decrease in body mass was observed (-2.05 kg [-3.37 : -0.73], -2.4% [-3.9 : -0.8], p = 0.006, η2 = 0.546). In contrast the accrual of lean mass during his period was 1.3 % [0.7 : 2.0] or 0.88 kg [0.44 : 1.32] per annum, with similar within-season fluctuations in fat mass. In conclusion, cyclical change in body composition occur within and between-season that belie change in body mass. Whilst cycling of fat mass persisted over consecutive seasons, the linear increase in lean tissue mass was a robust observation considered optimal for enhanced physical performance.