This paper has two main goals. First, I demonstrate how the peculiar morpho-syntactic properties of the theme NPs in Isbukun Bunun existential sentences can be derived under an expletive account. The properties under investigation include structural Case marking, the emergence of definiteness restrictions, and the resistance of theme NPs to Ā-extraction. Second, I argue for a small clause analysis of existential sentences in Isbukun Bunun. In particular, based on word orders, island effects, the comparison with possessive constructions, and the coordination facts, I argue that the existential predicate in Isbukun Bunun selects a small clause as its sole internal argument. I also discuss how the proposal developed for Isbukun Bunun might generalize to, and shed light on, the impersonal constructions in natural languages.