Interview tapes of adult Cubans from the Latin American Capital Cities Dialect Project were transcribed, focusing on the variability in the deletion of word-final consonants, especially /s/. The operation of the deletion rule for /s/ in Cuban Spanish is shown to be principally dependent on grammatical categories and surface syntactic function. In particular, it is shown that Labov's hypothesis that "whenever a final consonant is variably deleted the rule will operate more often... if it is an integral part of the word and not a separate morphome..." is too general. The deletion in Cuban Spanish is constrained by a functionalist condition, in this case, the pressure to preserve the singular/plural contrast in noun phrases. The /s/ most often deleted is the one preceded by a determiner which preserves a number marker. Other grammatical categories are unaffected. (Author)