We observed a birth in a group of Mexican mantled howler monkeys (Alouatta palliata) living under semi-free-ranging conditions on Agaltepec Island, Catemaco, Veracruz, Mexico. Although we could not quantify contractions, we were able to record a complete description of the sequence of events that resulted in a successful birth. Nine minutes passed from the release of the amniotic fluid to the total emergence of the infant. Although all group members were resting relatively close to the female when the birth occurred, none approached her until the postpartum period. Only then did several individuals briefly inspect the newborn and then resume their foraging activities. Am. J. Primatol. 65:93–98, 2005. © 2005 Wiley-Liss, Inc.