Previous research has shown that pre-aspiration can be a phonemic and a variable linguistic feature susceptible to linguistic and extra-linguistic influences. In the case of Welsh, previous exploratory work has found the presence of pre-aspiration (Ball 1984, Morris 2010, Spooner 2016, Iosad forthcoming), but the phonetic and phonological properties of this feature and its sociophonetic patterning in the language are not known. This article presents analyses of the variety of Welsh spoken in Bethesda (Gwynedd). It reports the frequency of occurrence of pre-aspiration, its duration, and noisiness. As well as describing pre-aspiration, it attempts to ascertain the extent to which this feature is influenced by linguistic and extra-linguistic factors. Wordlist data were analysed from 16 Welsh–English bilinguals from Bethesda (Gwynedd, North Wales). Speakers were aged between 16 and 18 years old and the sample was stratified by speaker sex and home language (either Welsh or English). The results indicate that pre-aspiration is frequent in both fortis and lenis plosives (the latter of which are typically devoiced in Welsh). In addition to a number of linguistic influences on its production, both speaker sex and home language were found to be significant predictors of variation for some measures. The results are discussed with reference to previous studies of pre-aspiration in other languages and work on phonetic variation in Welsh–English bilingual speech.