For patients, treatment of diabetes involves complex changes in basic behaviors and adherence to complicated regimens. Understanding the factors that enable patients to adhere to diabetes treatment is the first step to designing effective interventions. Researchers of diabetes care have postulated that increasing diabetic patients' participation in medical decision making during the doctor visit is likely to improve their adherence to self-care. However, a critical review of the impact of patient participation on diabetic patients adherence to self-care is absent from the literature. We review the subject of patient participation in medical decision making and its effect on adherence to self-care for patients with diabetes. We introduce a model of the determinants of adherence to diabetes self-care that incorporates the effects of patient participation in medical decision making. In this model, we suggest three ways that patient participation can affect adherence to self-care: 1) it may have a direct effect; 2) it may affect adherence to self-care indirectly by affecting patients' understanding of their treatment regimen or the fit of their regimen with their lifestyle; and 3) perceived omissions of participation can affect adherence to self-care indirectly through an effect on patient satisfaction. Research is needed to identify more clearly which components of patient participation affect adherence to self-care and in what ways. Distinguishing patient and physician behaviors that contribute to the process of patient participation would provide a means to develop specific behavioral interventions.