CPAP is an effective treatment for obstructive sleep apnea (OSA), though low adherence rates limit its benefits. Previous research has linked personality to a range of health behaviours including CPAP adherence. In keeping with these findings it was hypothesised that CPAP adherence would be positively correlated with conscientiousness and negatively correlated with emotionality. The present study also tested for an interaction between conscientiousness and emotionality as well as investigating the relationship between personality facets and adherence. Participants were 110 adults, diagnosed with OSA. After approximately one month's treatment, average nightly usage for the previous week was downloaded from the CPAP device. Participants also completed the HEXACO Personality Inventory – revised. Contrary to expectation, there was no significant relationship between CPAP adherence and conscientiousness or emotionality and no significant interaction. However, the diligence facet of conscientiousness showed a significant positive correlation with CPAP adherence (r = .23, p < .05). Unanticipated negative correlations were also found between CPAP adherence and agreeableness and two of its facets: gentleness (r = –.33, p < .01) and patience (r = –.22, p < .05). The results provide support for an association between CPAP adherence and personality. It is recommended that future research focus on facet level measurement, in particular the personality facets associated with conscientiousness and agreeableness.