Diagnosing specific language impairment (SLI) in monolingual children is a complex task, with some controversy regarding criteria. Diagnosis of SLI in bilinguals is made more complex by the lack of standardized assessments and poor understanding of clinical markers in languages other than English. There is an added complexity when one of the languages being acquired is an endangered one, where the domains of use and input are restricted, and where input is affected by convergence with the majority language. This article explores the challenge facing speech and language therapists and psychologists in diagnosing SLI in bilingual children acquiring Irish and English. Six speech and language therapists and four psychologists took part in semi-structured interviews exploring the impact of the bilingual environment, the nature of bilingual language impairment, current practices and the needs of these children. Thematic analysis was carried out and here three of the main themes emerging in the areas of assessment, the bilingual environment and characteristics of language impairment in this population are discussed. For assessment, an overriding theme was the requirement of standardized testing to secure additional educational and therapy resources for these children. However, because there are no standardized tests available in Irish, both professions end up translating existing English-based language and psychological assessments, using the norms provided to achieve standard scores. Both professions expressed strong dissatisfaction with this practice but saw little choice, given the Department of Education's approach to allocation of supports. Language impairment in Irish was characterized by lexical difficulties, particularly with verbs and prepositions, tense errors, and significant borrowing and code-switching with English. Other themes that emerged were the growing influence of English as the children became older, which affected both attitudes to the minority Irish language as well as the content and structure of the language itself. The implications for service provision for bilingual populations in general are outlined.