Parturition is a key process of mammalian reproduction that is rarely documented in New World monkeys because it often occurs at night. However, diurnal births have been recorded in several species. In howler monkeys (Alouatta spp.) they have often been observed during prolonged resting periods. Similarly, infanticide is a behavior observed quite infrequently. Infanticide in howler monkeys is often inferred from infant deaths or disappearances after group takeovers by nonresident male(s). Here we report the first observation of parturition and birth-related behaviors in the brown howler monkey (Alouatta guariba clamitans) and the likely attack on the infant that caused its death. The mother was a multiparous female that lived in a ca. 3-ha Atlantic forest fragment in southern Brazil with nine group mates. The behavior ("all occurrences") sampling method was used to record birth-related behaviors and social interactions. The parturition occurred during the day of 27 October 2013 during a feeding session. The female showed no sign of contraction or birth delivery posture. Parturition began apparently after matrix rupture and release of the amniotic fluid. Expulsion of the newborn occurred between 1 and 3 min later (the exact moment of delivery was not observed). Then, the female held and licked the newborn and began to ingest the placenta and the umbilical cord. The other group members continued feeding and had no interaction with the parturient during the preparturition and parturition events. The infant died ca. 35 days later as a consequence of injuries to his forehead and face, potentially caused by a conspecific bite. Because the adult and subadult males chased the female in the day that the infant's wounds were detected, we believe that one of them might have been the aggressor. We discuss this putative case of infanticide in light of the potential motivation of each male.