Mario Sitri competed at the 1956 Olympics in boxing and then in 1957 won a silver medal in the featherweight class at the European Championships, after which he turned professional. Sitri fought as a pro through 1968, with a career record of 33 wins, 25 losses and 2 draws. In 1959 he won the Italian bantamweight championship, and in 1961 the Italian featherweight championship, losing both titles after only a few months. In 1962 he regained the Italian featherweight crown, losing it again in his next bout two months later.
Italy