We compared responding to joint attention (RJA) in younger siblings of children with ASD (SIBS-ASD; n = 46) and younger siblings of children developing typically (SIBS-TD; n = 35). Children were tested between 12 and 23 months of age in a situation in which an experimenter directed the child’s attention to one of 8 targets. Each child responded to 10 different combinations of verbal and nonverbal cues containing varying levels of attention-specifying information. SIBS-ASD had significantly lower overall RJA scores than SIBS-TD. Moderately redundant cues were most difficult for SIBS-ASD relative to SIBS-TD; adding a point to moderately redundant cues improved RJA for SIBS-ASD, bringing them to a level of RJA commensurate with SIBS-TD.