Medication adherence is essential in preventing adverse intermediate outcomes, but little is known on hard outcomes. The aims of this study were to determine the 1-year adherence to oral antihyperglycemic drugs (OADs) and to predict the risk of subsequent health outcomes among (non)adherent patients with diabetes.Using a large Swiss healthcare claims database from 2011 to 2014, we identified all patients aged ≥18 years with diabetes and treated with at least 1 OAD prescription. Adherence to OADs was measured as the proportion of days covered (PDC) over 1 year and subdivided into 2 categories: adherent (PDC ≥ 80%), nonadherent (PDC < 80%). We estimated the relative risk of hospitalization and mortality at follow-up using multivariate Cox proportional hazard models.Based on a sample of 26,713 patients, adherence to OADs was quite low: 42% of the patients achieved a PDC of ≥80% during the 1-year observation period. A 7% reduction in the hospitalization risk and a 10% reduction in the risk of mortality could be observed in adherent patients compared to nonadherent patients (hazard ratio [HR], 0.93 [95% CI, 0.89-0.97]; HR, 0.90 [95% CI, 0.82-0.99]). Subgroup analysis showed that an intensified diabetes therapy had no significant influence on the risk of both outcomes in adherent patients.Poor medication adherence increases the risk of subsequent hospitalizations and premature mortality in patient with diabetes, regardless of disease severity and comorbidities. This emphasizes the need for an earlier identification of patients with poor medication adherence. The awareness of physicians and patients regarding the importance of adherence in diabetes treatment should be increased.