The nature and generality of the developmental association between phonological short-term memory and vocabulary knowledge was explored in two studies. Study 1 investigated whether the link between vocabulary and verbal memory arises from the requirement to articulate memory items at recall or from earlier processes involved in the encoding and storage of the verbal material. Four-year-old children were tested on immediate memory measures which required either spoken recall (nonword repetition and digit span) or recognition of a sequence of nonwords. The phonological memory-vocabulary association was found to be as strong for the serial recognition as recall-based measures, favouring the view that it is phonological short-term memory capacity rather than speech output skills which constrain word learning. In Study 2, the association between phonological memory skills and vocabulary knowledge was found to be strong in teenaged as well as younger children, indicating that phonological memory constraints on word learning remain significant throughout childhood.