The study investigated whether working memory capacity is related to the acquisition of a syntactic structure as it emerges in L2 speech. Following Information Processing Theory L2 speaking is conceptualized as a complex skill requiring both automatic and controlled processes for its execution. Controlled processes require attention, which is limited in working memory. L2 speech production and acquisition are explained in terms of the interplay of controlled and automatic processes as well as in terms of the operation of a dual code cognitive system made up of a rule-based and a memory-based system. Working memory is assumed to be involved in the execution of controlled processes operating in the rule-base system, which, in turn, are assumed to be at least partially responsible for the acquisition of a syntactic structure in L2 speech. Overall results show that working memory capacity is related to the acquisition of a syntactic structure in L2 speech. Linguistic accounts of L2 processing are used to complement and explain the acquisition of the syntactic structure. Results are discussed in terms of the linguistic and psycholinguistic complexity of the syntactic structure investigated in relation to working memory capacity, processing of form versus processing of meaning, the acquisition of a rule by the rule-based system, L1 and L2 linguistic variations and constraints in L2 speech production.