Therapeutic noncompliance is a major issue in health care, having important negative consequences for clinical outcome as well as for health-care costs. This paper reviews the literature on the economics of therapeutic noncompliance, identifies methodological shortcomings and formulates recommendations for future economic research in this area. Medication noncompliance was explored more extensively, as the majority of articles dealt exclusively with this aspect of therapy. Eighteen studies were assessed according to their definition and measurement of medication noncompliance, study design, and identification and valuation of costs and outcomes. Very diverse designs and often invalid methods for calculating costs were found. Medication noncompliance is often ill-defined and measured in an inaccurate way. The economic consequences of therapeutic noncompliance have rarely been investigated according to the standard principles of good economic evaluation. Six studies examined both costs and consequences of noncompliance in a cost-outcome description or a cost-benefits, cost-effectiveness or cost-utility analysis. Eight studies dealt with the economic value of compliance-enhancing interventions. In general, studies on the economic consequences of noncompliance lack methodological rigour and fail to meet qualitative standards. There is a clear need for more and better research on the impact of noncompliance, on the cost-effectiveness of interventions and the potential of compliance-enhancing interventions to improve patient outcomes and/or reduce health-care costs.