The Leones' successes have always been periodical: Their first championship came in 1952, 22 years after the beginning of BSN tournaments. They repeated as champions in 1954 (no tournament was held in 1953), but they did not win anymore championships until 1960. The 1960s were a glorious decade for the Leones, who repeated in 1961 and then won back to back to back titles in 1964, 1965 and 1966. Tex Winters, an assistant coach with the NBA Chicago Bulls championship teams of the 1990s, coached the Leones to their two 1950s titles, while Red Holzman was the main architech of the titles won from '64 to '66.
Even through the Leones had reknowned players such as Chemba Lanauze and others, they could not win a championship for 24 years after the 1966 title. In 1984 they reached rock bottom when it was discovered that they had proceeded against the BSN's rules to sign the aptly named David Ponce. Ponce was an American born Puerto Rican, and he had not spent the three years in Puerto Rico that are necessary for a BSN player to be nationalized, therefore, he was not eligible to play in the league. When this was discovered, a league wide scandal broke out, and the league determined to close the tournament that year by carrying out the Copa Olimpica championship instead of the normal championship finals. The Leones were excluded from participating in the Copa Olimpica.
The Leones started rebuilding, adquiring such players as Papote Agosto, Cesar Bocachica and Papirito Leon. With these players, the Leones, contended for the 1989 title, losing in seven games to Mario Morales and the Guaynabo Mets. With the adquisition of veteran Bobby Rios in 1990, however, the Leones returned to the finals, and they beat Guaynabo in a rematch. In 1992, coached by legendary Julio Toro, the Leones returned to the throne, beating the Capitanes de Arecibo for the title. A rubber match with Mario Morales and his Mets was played at the 1993 finals, and the Leones prevailed, beating the Mets four games to one.
Ponce took nine more years to win a title. In 2002, however, they beat the Vaqueros for the title in seven games. In 2003, the Leones signed former Vaqueros player Jerome Mincy, but they could not repeat as champions.