This study investigated the role of language exposure on vocabulary acquisition in Irish, a minority language in Ireland which is usually acquired with English in a bilingual context. Using a bilingual Irish-English adaptation of the MacArthur- Bates Communicative Development Inventories (Fenson et al., 2007) longitudinal parent-report data were collected from 34 children (19 girls and 15 boys) at 4-monthly intervals, resulting in 61 data-points between the ages of 24-36 months. Language exposure estimates (based on the Developmental and Language Background Questionnaire created for COST Action IS0804) indicated that while the caregivers spoke ‘mostly Irish’ to the children, both languages were used in most households. The sampled children’s vocabulary on the ICDI consisted of more Irish words than English, particularly for nouns, predicates and closed class words, although they knew as many verbs in English as in Irish overall. The pervasive influence of English was also seen in the high number of translational equivalents found. ANOVAs showed no significant effect of main caregivers’ Irish use on children’s Irish vocabulary, but a significant effect for caregivers’ use of English on English scores. Irish vocabulary scores did not differ significantly for those who were ‘always’ exposed to Irish compared to those with lower exposure rates to Irish. The conclusions are that the verb in acquisition of Irish (a noun-centred language with lexical verbs) is vulnerable, and could benefit from being a focus of language intervention programmes in this endangered language. The study also shows that caregiver language use gives only a limited view of the child’s language exposure, and that family language patterns need to be established in a minority language context. The results contributed to a larger crosslinguistic study on early vocabulary acquisition in bilingual children within Working Group 3 of the COST Action IS0804.