Introduction: Code-switching refers to the bilingual’s ability to switch languages within a conversation and within a sentence. This language-switching is both grammatically well formed and conforms to discourse/pragmatic constraints in proficient adult bilinguals who have acquired both languages in early childhood (‘early’ bilinguals). Bilinguals with aphasia due to stroke or other brain trauma may present with impaired language selection. Evidence of grammatical impairment of code-switching is less conclusive. The aim of this study was to investigate whether the code-switching of early bilingual adults with aphasia systematically differs from that of healthy bilingual adults on grammatical and discourse measures. Methods: A single case design was used to examine the code-switching of three early bilinguals with aphasia, in comparison to language- and age-matched controls. Code-switching was tested on three types of sentences (those with pronoun subjects, negation, whquestions) across four conditions (conversation, narrative recount, elicited sentence production, lexical selection). Participants completed a detailed test battery assessing lexical, syntactic and cognitive abilities in each language. Results: The results for participants with aphasia differed significantly from the controls on grammatical but not discourse measures of code-switching. Significantly more language mismatches were produced on all sentence types for elicited sentences. Performance on lexical selection tasks varied across participants with aphasia. Language selection in conversation and narrative recount did not differ between participants with aphasia and controls. Discussion: These results provide evidence of a dissociation between discourse impairment and grammatical impairment of code-switching, and change over time in the capacity to code-switch. For these bilinguals with aphasia, grammatical impairment of code-switching was evidenced in the presence of unimpaired language selection. The implications for cognitive models of language switching will be discussed.