Purpose: This study examined the effect of Vocabulary Acquisition and Usage for Late Talkers (VAULT) treatment on toddlers' expressive vocabulary and phonology. Parent acceptability of VAULT treatment was also considered. Method: We used a nonconcurrent multiple baseline single case experimental design with three late talking toddlers aged 21-25 months. The treatment was delivered twice weekly in 30-min sessions for 8 weeks by a rotating team of four speech-language pathologists. Toddlers heard three of their 10 strategically selected target words a minimum of 64 times in play activities each session. Expressive vocabulary and phonology was assessed pre-post, with parent interviews conducted posttreatment. Results: All toddlers increased production of target words and expressive vocabulary. Ambient expressive vocabulary size increased by an average of 16 words per week (range of 73-169 words learned over the treatment period). On a 20-item, single-word speech assessment, the toddlers' phonetic inventories increased on average from three to seven consonants, and five to eight vowels. Two toddlers used protowords pretreatment, which were replaced by recognizable attempts at words posttreatment. Parents reported the treatment was acceptable for the child and their family with future consideration of parent-based delivery of the treatment in the home. Conclusions: The results of this treatment provide further evidence of a model of intervention informed by the principles of implicit learning, and the interconnectedness of phonological and lexical learning. Investigation is required to establish the efficacy and feasibility of VAULT in clinical contexts.