We carried out a study of the social behavior and dominance hierarchy in three groups of crowned sifaka (Propithecus coronatus) in the Antrema Forest Station in north-west Madagascar. Data were collected from April to June 2009 and October to November 2009 using all-occurrence sampling. During 273 hours of observation, the majority of social behaviors observed were grooming interactions (39%), followed by agonistic behavior (25%), play (19%), scent-marking (9%), call-localization (5%) and approach (3%). A social hierarchy was maintained in the groups of P. coronatus, with females dominating the males. Although different groups of P. coronatus defended their territories against other neighboring groups of the same species, the most frequently observed outcome of intergroup encounters was tolerance. In addition, we detected no significant change of sifaka behavior during interspecific encounters with rufous brown lemur (Eulemur rufus) or with mongoose lemur (Eulemur mongoz), suggesting these two species live in total sympatry with P. coronatus.