BACKGROUND: This study investigated factors that predict adherence to prophylactic medication. The design was data driven and aimed to expose the most prominent predictors of adherence. METHODS: A cross sectional sample of 24 males and 41 females, aged between 19 and 76 years, completed demographic questions, Medication Adherence Report Scale, Multidimensional Health Locus of Control Scale, Attitude towards Doctors and Medicine Scale, Eysenck Personality Questionnaire Revised (short scale) and the Short Form 36 Health Survey. RESULTS: Negative attitudes toward doctors, low mental health and chance health locus of control explained 33.2% of the variance in self reported medication nonadherence. DISCUSSION: That negative attitudes to doctors was a stronger predictor of nonadherence than side effects or medication cost was unexpected. Many studies have reported side effects and cost as primary reasons; however, these studies often do not assess the patient-doctor relationship.