Sin Piedad (2004) (Spanish for "No Mercy") was an annual professional wrestling major event produced by Consejo Mundial de Lucha Libre (CMLL), which took place on December 17, 2004 in Arena México, Mexico City, Mexico and replaced CMLL's regular Friday night show Super Viernes ("Super Friday"). The 2004 Sin Piedad was the fifth event under that name that CMLL promoted as their last major show of the year, always held in December. The main event of the show was a tag team Lucha de Apuestas ("bet match") between the team of Pierroth and Vampiro Canadiense and Los Hermanos Dinamita (Cien Caras and Máscara Año 2000). Both teams risked their hair on the outcome of the match, with the losing team being shaved totally bald after the match. The show included five additional matches, including a match for the Mexican National Trios Championship.

The Mexican wrestling company Consejo Mundial de Lucha Libre (Spanish for "World Wrestling Council"; CMLL) has held a number of major shows over the years using the moniker Sin Piedad ("No Pity" or "No Mercy"). CMLL has intermittently held a show billed specifically as Sin Piedad since 2000, primarily using the name for their "end of the year" show in December, although once they held a Sin Piedad show in August as well. CMLL has on occasion used a different name for the end-of-year show but Sin Piedad is the most commonly used name. All Sin Piedad shows have been held in Arena México in Mexico City, Mexico which is CMLL's main venue, its "home". Traditionally CMLL holds their major events on Friday Nights, which means the Sin Piedad shows replace their regularly scheduled Super Viernes show. The 2004 Sin Piedad show was the fifth show to use the name.

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