This article deals with some questions of case morphology in Baltic and their theoretical implications. The Latvian instrumental, which has coalesced with the accusative in the singular and the dative in the plural, causes notorious problems: although facts of prepositional government (the rise of differentiated prepositional government along the number opposition) show that the instrumental has effectively ceased to exist, the accusative singular and dative plural forms arising from it continue, albeit to a limited extent, to perform their former functions. Similar facts are adduced from Old Lithuanian, in which some local cases have entered a complementary distribution along the animacy vs inanimacy opposition without coalescing. It is well known that, diachronically, distributional patterns in the paradigm reflect morphosyntactic rules, but it is argued here that this may hold synchronically as well. Such facts as adduced here from Baltic cannot be explained at a purely morphological level within a paradigm-based approach, and in some instances distributional patterns in case paradigms must be allowed to be regulated by morphosyntax. This creates problems for the autonomy of morphology, and for the distinction between “syntactic” and “morphological” case.