Performance trends in breaststroke swimmers competing at world class level in pool competitions are well investigated for elite swimmers, but not for age group swimmers. This study investigated trends in participation, performance and sex difference in performance in a total of 35,143 (16,160 women and 18,983 men) age group breaststroke swimmers aged 25-29 to 95-99 years competing in the Fédération Internationale de Natation (FINA) World Masters Championships between 1986 and 2014. Trends in participation were analysed using linear regression analyses and trends in performance were investigated using mixed-effects regression analyses with sex, distance and calendar year as fixed variables. Women and men improved performance in all age groups. For age groups 25-29 to 85-89 years, men were faster than women. For age groups 90-94 to 95-99 years, men were not faster than women. Sex and distance showed a significant interaction for all distances in age groups 25-29 to 80-84 years. In 50 m, women reduced the gap to men in age groups 40-44 to 70-74 years and in 100 m and 200 m, women reduced the gap in age groups 50-54 to 60-64 years. In summary, (i) women and men improved performance in all race distances and in all age groups, (ii) men were faster than women from 25 to 89 years, but not from 90 to 99 years, and (iii), women reduced the gap to men between ~40 and ~75 years, but not in younger (<40 years) or older (>75 years) age groups. Based on these findings for a time period of nearly 30 years, we may assume a further increase in participation and a further improvement in performance in the near future in age group breaststroke swimmers competing at world class level.