Background Medication and dietary nonadherence are precipitating. factors for heart failure (HF) hospitalization,however, the characteristics, outcomes, and quality of care of patients with nonadherence are unknown. Recognizing features of nonadherent patients may provide a means to reduce rehospitalization for this population. Methods GWTG-HF registry data were collected from 236 hospitals and 54,322 patients from January 1, 2005 to December 30, 2007. Demographics, clinical characteristics, in-hospital outcomes, and quality of care were stratified by precipitating factor for HF admission. Multivariate logistic regression analysis was used to determine the association of nonadherence with length of stay (LOS) and in-hospital mortality. Results Clinicians documented dietary and/or medication nonadherence as the reason for admission in 5576 (10.3%) of HF hospitalizations. Nonadherent patients were younger and more likely to be male, minority, uninsured, and have nonischemic HF. These patients had lower ejection fractions (34.9% vs 39.6%, P < .0001), more frequent previous HF hospitalizations, higher brain natriuretic peptide levels (18 13 vs 1371 pg/mL, P < .0001), and presented with greater signs of congestion. Despite this, nonadherent patients had shorter LOS (odds ratio 0.94, 95% CI 0.92-0.97) and lower in-hospital mortality (odds ratio 0.65, 95% CI 0.51-0.83) in multivariate analysis. Although nonadherent patients received high rates of Joint Commission core measures, rates of other evidence-based treatments were less optimal. Conclusions Nonadherence is a common precipitant for HF admission. Despite a higher risk profile, nonadherent patients had lower in-hospital mortality and LOS, suggesting that it may be easier to stabilize nonadherent patients by reinstituting sodium and/or fluid restriction and resuming medical therapy. (Am Heart J 2009;158:644-52.)