In general, the Malayic languages of Sumatra show a vowel phoneme inventory that is either equal to or greater than that of the five phonemes in Standard Malay/Indonesian (not including the so-called pepet vowel); dialects of Jambi Malay, Palembang Malay, and Minangkabau all show five phonemes. However, from recent fieldwork in Besemah, a Malayic language in the highlands of southwest Sumatra, I shall describe an inventory that evinces the smallest number of vowel phonemes in any Malayic language of Sumatra described to date. That is, Besemah has three vowel phonemes. Nevertheless, the analysis of Besemah vowel phonemes is not straightforward; vowel lowering in closed syllables, vowel harmony, and raising of the word-final low central vowel all cloud the analysis of a three-vowel system. Furthermore, Besemah currently is experiencing intense pressure from other standard and nonstandard varieties of Malay/Indonesian, which demonstrates how intense contact involving diglossia and increasing bilingualism in these other varieties of Malay/Indonesian appear to be leading to an emergence of mid vowels in Besemah.