We analyzed immature-to-mother social distance (juveniles and non-nursing infants) in two Mexican mantled howler monkey (Alouatta palliata) troops inhabiting a tropical rainforest fragment (40 ha) at Los Tuxtlas, Veracruz, Mexico. During July and August of 2000 and 2001 we applied an instantaneous sampling method (317 hr) to record the behaviors of the immatures and their mothers, as well as distances (ordinal scale) between immatures and their mothers (IMD), and between immatures and nonmother individuals (INMD). Immatures were generally less than 5 m away from any individual of the troop. Social distance was influenced by the different behaviors of both mothers and immatures, with the shortest distances occurring during rest (IMD <5 m in 94% of all instantaneous samples) and the longest during exploration (21%≥10 m) and play (26%≥10 m). When IMD increased, we found a higher percentage of records <5 m to other individuals, particularly with the probable father. When the variation in distance to the mother and to other individuals in the troop was considered, the immature animals' distance to other troop members depended on the immatures' age and type of behavior. Overall, these results suggest that in this low-activity species the development of the immature is associated with a complex set of relationships with other troop members. Am. J. Primatol. 69:1–9, 2007. © 2006 Wiley-Liss, Inc.