Poor medication adherence is a widespread problem that undermines the potential benefits of medical treatment. Typical adherence rates among chronic disease patients are approximately 50%, and these low adherence rates have a substantial economic impact, estimated at $100 to $300 billion annually. Nonadherence to immunosuppressants among transplant recipients is surprisingly frequent, and the consequences are serious. Among adult renal transplant patients, the median rate of nonadherence is approximately 22% and is associated with acute rejection episodes and approximately 36% of all graft losses. In the United States, nonadherence results in an estimated 903 episodes of acute rejection and 1319 renal transplants failures annually, costing approximately $15 million and $100 million, respectively. Drug regimen complexity is known to impact adherence. Research demonstrates an inverse relationship between dosing frequency and medication adherence in various chronic diseases, with once-daily dosing resulting in the highest adherence rates. Reducing the dosing frequency may positively impact both clinical and patient-reported outcomes, as well as health care costs. However, the increased costs of less frequently administered drugs must be outweighed by the net savings achieved through improved adherence rates and better health outcomes. If trends among patients with chronic diseases apply, once-daily dosing regimens may improve adherence rates by approximately 6% to 14% among renal transplant patients and could substantially reduce the number of acute rejection episodes and graft failures, although the exact economic impact is difficult to estimate. Further research into adherence issues in transplant patients and the potential clinical and economic benefits of once-daily dosing of immunosuppressants is warranted.