The aim of this paper is to analyse some aspects of development of Basque as a second language (L2) in children for whom Spanish is their first language (L1) who attended immersion school in Basque in a Spanish-speaking sociolinguistic context. Data consist of oral story retellings produced in a classroom setting where the same children participated at ages 5, 8 and 11. Another group of children for whom Basque was the L1 and who lived in a strong Basque-speaking environment also took part in the study. Two aspects are analysed in the stories: lexical difficulties and the production of text organisers. According to the results, the Basque L2 children seemed to have acquired a linguistic competence quite comparable to L1 capacity: the lexical aspects studied show a clear development in L2, since lexical gaps were frequent at age 5, diminished at age 8 and were practically non-existent at age 11. The production of text organisers also shows a clear developmental pattern and, with increasing age, the children produced a higher variety of text organisers, providing precise temporal links to different segments of the story. It is concluded that Basque immersion seems to foster the development of Basque L2 in contexts where the use of Basque is quite reduced.