At the European championships, Isser won six medals in the women's singles event and one in the doubles event. This included five straight golds (Women's singles:1952–1955, Doubles: 1954), one silver (Women's singles: 1956), and one bronze (Women's singles: 1951). Maria's European gold in the doubles event in 1954 with her brother Josef was the first time a woman ever won a medal in a doubles event at a World Championships, Winter Olympics, or European Championships until the debut of a mixed team event at both the European and World Championships in the late 1980s. Next year Maria and Josef finished at 2nd place in the doubles event at the 1955 World Championships. In the 1958 World Championships, the silver and bronze pairs from Poland included one woman each.