A field study of the Lutong, (Presbytis cristatus) was conducted in Malaya. Lutong troops were observed for more than 1000 hours and were found to be markedly territorial. Only one control male lives in each troop and he actively defends the territory against incursions by other lutong males. Each troop moves slowly through its territory feeding and resting and comes into frequent visual contact with adjacent troops. Each troop is a well organized social unit but only the control males show consistent hostility to one another when troops meet. Grooming, play, sexual responses, maternal behavior and agonistic episodes are described as well as travel, feeding and diurnal patterns. These patterns appear similar to those reported in other Presbytis species, but contrast markedly with macaque and baboon reports. Differences in behavior between species of Presbytis do not exceed differences reported in the same species by different observers in different areas.