Basque weak quantifiers optionally agree with the inflected verb in number. This papers’ main aim is to study the dialectal variation shown by this phenomenon. The study will show that it is necessary to differentiate at least three systems: the central-western system, one that we will call the transition system (Lapurdian), and the eastern system (Souletin). The central-western system allows the presence of non-agreeing weak quantifiers in every case-marked position (ergative, dative or absolutive); the transition system does not allow it with ergative case arguments; and the oriental system allows it only with absolutive case arguments. In the latter system, the distribution of non-agreeing quantifiers is identical to that of bare nouns: bare nouns are only possible in those positions where absolutive case is assigned.