In this paper we offer a first systematic account of the noun class system of Ngwi, a West-Coastal Bantu language spoken in the Democratic Republic of the Congo. First, we describe the synchronic system of noun class prefixes and the agreement patterns they trigger on constituents of the noun phrase and the verb. Second, we provide a diachronic analysis of the innovations the synchronic Ngwi noun class system underwent with respect to the noun class system reconstructed for the most recent common ancestor of all Narrow Bantu languages. Finally, we compare the morphological innovations found in the Ngwi noun class system with those identified in the noun class systems of other West-Coastal Bantu varieties and assess whether some of these could be diagnostic for internal classification within this western Bantu branch.