Using the Nepali National Corpus, a collocation-based technique is applied to the categorization of Nepali postpositions. Ergative le, accusative lāī, and genitive ko/kā/kī are frequently considered in the literature to be part of the Nepali nominal inflection paradigm, but opinion differs on other postpositions. The most significant collocations of several postpositions are examined for patterns that characterize postpositions as a category or categories. Two overarching patterns — collocation with semantically coherent nouns, and collocation with words for which the postposition functions as a subcategorizer — are identified. The analysis of some postpositions as part of the nominal paradigm is not supported by the analysis of these patterns. However, postpositions traditionally seen as part of the nominal paradigm do collocate more with non-lexical words, especially pronouns.