This article discusses the relationship between Milang, a little-known language of the Eastern Himalayan region, and the Tani branch of Tibeto-Burman languages with which it has been provisionally aligned. Reviewing this alignment, we find little positive evidence in its favor. Bringing new linguistic and cultural field data to bear on the question, we conclude that Milang contains much linguistic material that cannot possibly be directly inherited from the ancestor of all Tani languages proper (i.e., “Proto-Tani”). We therefore suggest that material shared with Tani languages proper is either reconstructible to an earlier, pre-Proto-Tani stage, or has been subsequently acquired through contact with Eastern Tani languages. Material not shared with Tani languages proper may reflect an unknown substrate. While our resulting re-classification of Tani languages is thus in a sense quite minor, it has some important implications: first, that cultural and linguistic diversity in the Eastern Himalaya was probably much greater than has been assumed, and second, that sociolinguistic and cultural information are critical factors in the evaluation of linguistic subgrouping proposals and the reconstruction of pre-history.