The objective was to identify the degree to which illness perceptions and medication beliefs explain variations in reported adherence to medication prescribed for the treatment of non-malignant chronic pain and to test the applicability of an extended version of the self-regulatory model to the chronic pain population. A cross-sectional design included 217 clinic patients completing validated questionnaires assessing their illness perceptions, medication beliefs and reported adherence to medication. Perceptions of illness (pain) as chronic, uncontrollable and unremitting were associated with greater adherence, fewer medication concerns and a belief that treatment was necessary. Structural equation modelling supports an extended SRM for chronic pain. It suggests that patients holding perceptions of serious consequences of pain and high emotion levels have more concerns about medication and are less adherent. Perceptions of serious illness consequences are also associated with stronger beliefs about the necessity of medicines and greater adherence. Beliefs about illness and medication are associated with adherence to treatment in chronic pain and this can be explained by an extended SRM. Results are preliminary and require replication. Further studies should explore the role that emotion has on coping strategies in chronic pain. Interventions should focus on altering unhelpful beliefs that reduce adherence.