Sociedade União 1º de Dezembro is a sports club from Sintra, Portugal. The football section of the club was founded on 6 April 1938, the women's football section in 1995. The men's football team plays in the Segunda Divisão. The women's football team plays in the national top league, the Campeonato Nacional and is dominating the competition in recent years. After the first championship title in 1999-2000, the team won every season from the 2001-02 season onwards for now eleven championships in a row. With their twelfth title in 2012 they became Portugal's record champion.
In the UEFA Women's Cup they have not gone past the 1st qualification round. In the 2009–10 and 2010–11 Women's Champions League they competed in the qualifying round.