Relations between restricted and repetitive behavior at age 26 months and children's concurrent (N = 203) and later (n = 161) social cognition and language development were investigated. Restricted and repetitive behavior was assessed using two scales: sensory and motor repetitive behaviors and rigidity/routines/restricted interests. Language was assessed at ages 26 and 51 months; social cognition was assessed at ages 26 (symbolic play) and 51 and 61 months (theory of mind). Sensory and motor repetitive behavior was negatively related to children's (a) language performance at 26 and 51 months, (b) instructed symbolic play at 26 months, and (c) theory of mind performance at 51 and 61 months. Path analyses showed that children's sensory and motor repetitive behavior at age 26 months was related to lower receptive verbal ability and theory of mind at 51 months, which led to lower theory of mind at 61 months. Rigidity/routines/restricted interests at 26 months were unrelated to concurrent and later social cognition and language. These results are discussed in terms of the pathways via which sensory and motor repetitive behavior might impact negatively on development.