Background: Poor adherence to medical treatment is one of the main reasons why patients do not achieve the full benefits of their therapy. It also has a substantial financial weight in terms of money wasted for unused medication and increased healthcare costs including hospitalization due to clinical complications. Objective: To provide an overview and examples of the financial and economic consequences of poor adherence to treatment, techniques and devices for monitoring adherence and interventions for improvement of treatment adherence. Results: New electronic devices with monitoring features may help to objectively monitor patients' adherence to a treatment regimen that can help a healthcare professional determine how to intervene to improve adherence and subsequent clinical outcome. Interventions that aim to enhance adherence may confer costeffectiveness benefits in some indications and settings. The nature of the intervention(s) used depends on a range of factors, including patient preference, therapy area and cost of the intervention. However, there is a pressing need for rigorous trials, as current studies often have major flaws in the economic methodology, especially in terms of incremental analysis and sensitivity analysis. Limitations: This review has focused on a limited number of therapeutic areas as coverage of a more extensive range of diseases may be beyond the scope of such a summary. Nevertheless, the examples are representative of the challenges encountered in many other diseases. Conclusions: The clinical and economic consequences of non-adherence and interventions to improve compliance reflect the nature and severity of non-adherence, as well as the pathophysiology and severity of the disease. Interventions that aim to enhance adherence may confer cost-effectiveness benefits in some indications and settings, and good adherence can help payers and providers contain costs by extracting maximum value from their investment in therapies.