I studied gray woolly monkeys (Lagothrix lagotricha cana)in an undisturbed central Amazonian terra firme forest near the headwaters of the Urucu river Tefv© Amazonas Brazil (5¬850‚ÄôS 65¬816‚ÄôW). I report the diet and feeding ecology of a group of 39‚Äì41 individuals based on systematic feeding observations obtained during 11 months. Woolly monkeys are primarily frugivorous; mature fruits and young seeds account for 83 and 7% of 3298 feeding records respectively. On a seasonal basis however they relied heavily on young foliage (16%) seed-pod exudates (6%) and flowers (3%) particularly during the greatest annual period of ripe fruit scarcity as determined by a phenological survey. Animals represent only 0.1% of their year-round diet and they spent little time capturing arthropods and other prey items. Although at least 225 plant species belonging to 116 genera and 48 families are in their diet the three top-ranking families (Moraceae Sapotaceae and Leguminosae) account for 43% of their food species and 63% of the time they spent feeding on a year-round basis. I compare the feeding ecology and diet of L. 1. canain the Urucu and other taxa of Lagothrixin upper Amazonia ‚Äî the last large-bodied Neotropical primates to be studied ‚Äî to those of other ateline genera: Atelesand Brachyteles.