This study examines two components of lexical acquisition and phonological development that occur during the first 50-word stage of language development in neurotypical (NT) children. One component is how children learn words based on their existing speech sound inventories (i.e., in-phonology and out-of-phonology word learning). The other component is the relationship between the children's number of words and the number of phonemes in their speech sound inventories. The goal of this study is to determine if the same two components occur in children with autism spectrum disorders (ASDs) who are older than their NT peers but are in the same stage of lexical development. This study involved 20 minimally verbal children with ASDs, ages 28-72 months, who produced five to 50 spoken words. The children's spoken words were obtained from the MacArthur-Bates Communicative Development Inventories. The speech sound inventories were obtained from the utterances produced during assessment/play sessions with the children. The children's spoken words from the Communicative Development Inventories (CDI) were categorized as either in-phonology or out-of-phonology based on whether the words began with a phoneme in the child's existing speech sound inventory. Additionally, the children's number of spoken words on the CDI was compared to the number of phonemes in their speech sound inventories. The children in this study produced in-phonology words more often than out-of-phonology words (z = -3.922; p < .001). Moreover, there was a moderate positive correlation between the children's number of spoken words and the number of phonemes in their speech sound inventories (r = .534, p = .019). The relationship between lexical acquisition and phonological development appears to exist for the children in this study, who are in the first 50-word stage of development. Clinical implications for increasing the expressive language of children with ASDs were discussed.