The study examines the sustainability status of Sarawak indigenous languages through a survey on adolescents' language use using the Expanded Graded Intergenerational Disruption Scale (EGIDS). The specific aspects examined were: the presence of ethnic languages in relation to other languages in selected domains of language use; the adolescents' use of the ethnic language across generations in the family domain; language use patterns of different indigenous groups; and demographic variables which influence use of the ethnic languages for the indigenous groups. The language use survey involved 568 indigenous adolescents in six schools in Sarawak, Malaysia. The results show that the domains of the ethnic language are shrinking because of the growing presence of Malay varieties (Standard Malay and Sarawak Malay), particularly for smaller groups. The ethnic language is still strong in the family and religious domains but has little place in the education and mass media domains. In the ethnically heterogeneous public domains of transaction and friendship, the ethnic language is for intra- and Malay varieties for inter-ethnic communication. The demographic characteristics which predict sustained use of the ethnic language are the vitality of the ethnic group, rural locality and lower socio-economic status. (Contains 6 tables.)