The present study investigates the effects of two subsequent learning contexts, formal instruction (FI) at home and a 3-month stay abroad (SA), on vocabulary acquisition in English as a foreign language (EFL) writing and speaking. Data were collected from 30 Catalan/Spanish learners of English before and after each learning period using a written composition and an oral interview. These samples were examined in terms of quantitative measures of lexical proficiency in the domains of diversity, sophistication, density and accuracy. Native-speaker baseline data were also obtained through the same tasks for comparison purposes. Results reveal that SA is particularly beneficial for written productive vocabulary, and less so for oral, and that progress occurs especially in lexical diversity. FI, however, shows a modest effect on the improvement of oral productive vocabulary and affects namely lexical sophistication.