The diet of a group of six brown howlers was studied weekly during 12 months in a reserve of 250 ha of secondary mesophytic semi-deciduous forest. The phenology of 186 trees of 72 species and 29 families was monitored simultaneously. Scan sampling was used to record the diet from dawn until dusk on a total of 60 days of observation yielding 718 hr of animal-observer contact and 2943 feeding scans. The diet was composed of leaves (73%) flowers (12%) and fruits (5%) from 68 identified plant species.Celtis iguanae Cassia ferruginea andInga spp. were the main food sources accounting for approximately 50% of the diet. Young leaves (59%) were preferred to mature leaves (31%) trees contributing 56% and lianas 41% of the leaf diet. The ingestion of young leaves was correlated to the availability of these items however the correlations were not significant for flowers and fruits. The diet was poorer in fruits and richer in young leaves of lianas in comparison to other howler monkey species studies probably as a consequence of the liana abundance in this forest fragment.