Background: Spoken and gestural communication proficiency varies greatly among autistic individuals. Three studies examined the role of oral- and manual-motor skill in predicting autistic children's speech development. Methods: Study 1 investigated whether infant and toddler oral- and manual-motor skills predict middle childhood and teenage speech fluency; Study 2 verified those early infant and toddler predictions with historical home video; and Study 3 assessed the relation between autistic children's current-day oral-motor skill and their speech fluency. Results: Infant and toddler oral-motor and manual-motor skills inter-correlated significantly, distinguished autistic children (N = 115) from typically developing children (N = 44), and distinguished autistic children whose current-day speech was minimally fluent (N = 33), moderately fluent (N = 39), and highly fluent (N = 39). These results were corroborated by analysis of historical home video (N = 32) and verified with current-day assessment (N = 40). Conclusions: The prominent associations among early oral- and manual-motor skills and later speech fluency bear implications for understanding communication in autism. For instance, these associations challenge the common assumption (made even in diagnostic criteria) that manual modes of communication are available to autistic individuals--if simply they choose to use them. These associations also highlight a potential confound from manual-motor skills when assessing autistic cognition, receptive language, and "nonverbal" social communication.