Nonadherence to medical regimens is a major problem in health care. Distinguishing between intentional nonadherence (missing/altering doses to suit one's needs) and unintentional nonadherence (forgetting to take medication) may help in understanding nonadherence. Participants with respiratory conditions completed an anonymous questionnaire about (i) nonadherence; (ii) reasons for and against taking medications; and (iii) perceived style of the consultation in which their medication was first prescribed, as well as demographic and clinical variables. Consistent with the hypotheses, intentional nonadherence is predicted by the balance of individuals' reasons for and against taking medication as suggested by the Utility Theory, where these reasons include only those which the individual considers relevant and on which he/she focuses. Unintentional nonadherence is less strongly associated with decision balance, and more so with demographics. The research highlights the importance of (a) treating intentional and unintentional nonadherence as separate entities and (b) assessing individuals' idiosyncratic beliefs when considering intentional nonadherence.