OBJECTIVES: To evaluate primary nonadherence [PNA] to cholesterol medications and compare health care outcomes between primary adherent and nonadherent patients. METHODS: This retrospective cohort study identified all patients who were treatment-naïve to antihyperlipidemics patients with at least one new cholesterol prescription written during the period of December 1, 2009 to February 28, 2010.  PNA was defined as the failure to fill a prescription within 90 days of when it was written [index date].  Patients were followed for 18 months after the index date for healthcare outcomes of low-density lipoprotein [LDL] values, cardiac/stroke events, ER visits and all-cause or cardiac/stroke-related hospitalizations. Descriptive statistics were used to compare baseline characteristics and health care outcomes between primary adherent and nonadherent patients. Cox proportional hazard models were used to estimate the hazard ratio [HR] as a measure of the relative risk of each event in the primary nonadherent in comparison to the primary adherent after controlling for patient and physician characteristics.  Patients were censored at the end of the follow-up period. RESULTS: A total 17,400 patients were identified during the study period and 15% were primary nonadherent.  At baseline, primary nonadherent patients were sicker than primary adherent patients with significantly higher Charlson comorbidity index values, prescription use, ER visits and hospitalizations in the prior year.  LDL values decreased after the index date for both groups, but primary adherent patients had a significantly greater decrease in LDL values on average [-37.2 vs. -14.9 (p<0.0001)].   After adjusting for baseline covariates, the resulting HR (95%CI) was 0.83 (0.69, 0.99) for cardiac/stroke events, 0.99 (0.91, 1.09) for ER visits, 0.87 (0.77, 0.99) for all-cause hospitalization, and 0.72 (0.44, 1.12) for CV-related hospitalization. CONCLUSIONS: Primary nonadherent patients experienced smaller decreases in LDL values, but were not found to be at increased risk for cardiac/stroke events, ER visits or hospitalization during the follow-up period.