One key criterion when creating a representation of the lexicon of any language within a dictionary or lexical database is that it must be decided which groups of idiosyncratic and systematically modified variants together form a lexeme. Few researchers have, however, attempted to outline such principles as they might apply to sign languages. As a consequence, some sign language dictionaries and lexical databases appear to be mixed collections of phonetic, phonological, morphological, and lexical variants of lexical signs (e.g. Brien 1992) which have not addressed what may be termed as the lemma dilemma. In this paper, we outline the lemmatisation practices used in the creation of BSL SignBank (Fenlon, Cormier et al. 2014), a lexical database and dictionary of British Sign Language based on signs identified within the British Sign Language Corpus (http://www.bslcorpusproject.org). We argue that the principles outlined here should be considered in the creation of any sign language lexical database and ultimately any sign language dictionary and reference grammar.