Little is known for pacing profiles in age groups cross-country skiers. The aim of the present study was to examine the effect of sex, age and calendar year on pacing strategies in the largest ski marathon in the world. All finishers (n = 66,435) in 'Vasaloppet' from 2012 to 2016 were examined for 12 different age groups (G). There was an association between age group and sex (χ^2 = 1091.1, P ＜ 0.001; Cramer's V = 0.13, P ＜ 0.001), where the men-to-women ratio in each age group ranged from 3.29 (in G_(20)) to 64.36 (in G_(70)). A between-within subjects analysis of variance (ANOVA) showed a sex × split interaction of small magnitude (P ＜ 0.001, η^2 = 0.019) on speed (v) indicating sex-specific pacing strategies. A main effect of sex on v was observed (P ＜ 0.001), where men were faster than women (12.5 ± 3.3 versus 10.3 ± 2.4 km．h^(-1), respectively). There was also a main effect of split on v of large magnitude (P ＜ 0.001, η^2 = 0.517), where all eight splits differed (v_2 ＞ v_3 ＞ v_8 ＞ v_5 ＞ v_4 ＞ v_7 ＞ v_6 ＞ v_1). In women and men, age groups differed (small magnitude) for v (P ＜ 0.001, η^2 = 0.015 and η^2 = 0.031, respectively), with the fastest v observed in G_(21) and G_(40), respectively. In women and men, an age group × split interaction on v of trivial magnitude was observed (P ＜ 0.001, η^2 = 0.005 and η^2 = 0.007, respectively). Based on these findings, it was concluded (i) a relatively low participation of women with increasing age, (ii) different pattern of pacing in women and men, and (iii) the age of the fastest v differed by sex.