We present an ethogram for golden-backed uakaris (Cacajao melanocephalus), based on observations in the field and on a captive individual. We also provide additional observations on the ecology of the wild animals. We studied 3 free-living groups (maximum counts of 5, 15, and 26 individuals) during two wet-seasons (March-July 2007 and January-June 2008) in the flooded igap forest of JaA(0) National Park, Amazonas, Brazil. The groups lived in close proximity but never mixed, because river channels separated them. Groups showed fission-fusion behavior, subgroup sizes varied within groups, and we observed 13 different subgroup compositions. The areas used by the groups were ca. 0.82, 2.35, and 2.45 km(2). We defined a total of 9 behavioral categories. In the wild, the amount of time allocated to the behaviors traveling and foraging/feeding differed between months, but we found no difference in the amount of time devoted to behavioral categories across 3 periods of the day, possibly as a result of the patchy and unpredictable distribution or availability of food patches. Further, the activity patterns varied among groups, perhaps as a reflection of the different group sizes and compositions and different range sizes. We recorded 34 feeding items for wild golden-backed uakaris between January and June 2008, mostly fruits and seeds. No significant variation in the number of different food types occurred across months. We recorded 6 primate species in the study areas. The uakaris neither mobbed nor fled from any other primate species, with the exception of white-fronted capuchin monkeys (Cebus albifrons). In addition, golden-backed uakaris sometimes fled when seeing giant otters (Pteroneura brasiliensis), perhaps indicating that the otters are potential predators of the monkeys. The ethogram and behavioral data provided here increase knowledge of the behavioral ecology of the elusive golden-backed uakari, and will facilitate future comparative studies.