Neuropsychological theories raise the question if in late bilinguals with dementia of the Alzheimer type (DAT), the second language (L2) may be more impaired than the first (L1). We compared language performance in different tasks of oral comprehension (semantic and syntactic) and production (naming, repetition and fluency) in L1 and L2 in a group of 13 late proficient bilinguals wit DAT immersion, and a matched control group of 12 healthy late bilinguals. Two-way mixed repeated-measure ANOVAs with factors Language and Group revealed main effects of Group (p < .05) indicating that DAT affects all aspects of language. There was no Group × Language interaction, suggesting that DAT affects both languages similarly. Our study thus shows that neurodegenerative diseases affect L1 and L2 in a parallel manner, particularly at the levels of semantic, lexical and syntactic processing. These results speak in favour of a shared L1 and L2 network in late bilinguals.