Within the field of SLA, the incidence of nativelikeness in second language (L2) speakers has typically been explained as a function of age of acquisition. An alternative interpretation, however, is that L2 learners do not attain nativelike proficiency because of first language (L1) maintenance. This interpretation has nevertheless remained mostly theoretical due to the lack of empirical evidence. This study sets out to address the role of L1 proficiency in L2 ultimate attainment by examining L1 and L2 proficiency in 30 early L1 Spanish-L2 Swedish bilinguals. Language proficiency was assessed through grammaticality judgment tests and cloze tests, and additional data on language aptitude were collected through the Swansea Language Aptitude Test (v.2.0; Meara, Milton, & Lorenzo-Dus, 2002). The results showed positive correlations between nativelike L1 and L2 behavior. Additionally, it was found that language aptitude was positively correlated with nativelike L1 and L2 performance. In view of these findings, it is suggested that (a) L1 maintenance does not hamper L2 nativelikeness and (b) language aptitude is an important factor for bilingual ultimate attainment.