Acute decompensated heart failure (ADHF) has emerged as a major public health problem, and HF has become the leading cause of hospitalization in persons over 65 years of age. It is estimated that there are 6.5 million hospital days attributed to ADHF each year. Patients hospitalized with ADHF face a substantial risk of readmission, as high as 50% by 6 months after discharge. Despite the large number of patients hospitalized and this substantial risk, data on these patients have been limited and there has been little effort to improve the quality of care for patients hospitalized with ADHF. The Acute Decompensated Heart Failure National Registry (ADHERE) was designed to bridge this gap in knowledge and care by prospectively studying the characteristics, management, and outcomes of a broad spectrum of patients hospitalized with ADHF. Participating community and university hospitals identified patients with a primary or secondary discharge diagnosis of HF and collected medical history, management, treatments, and health outcomes via secure Web browser technology. As of October 2004, more than 160,000 patients from 281 hospitals have been enrolled. These patients differ substantially from those typically enrolled in randomized clinical trials. Initial data from the ADHERE registry have provided important insights into the clinical characteristics, patterns of care, and outcomes of patients with ADHF. ADHERE has documented significant delays in diagnosis and initiation of ADHF therapies as well as a substantial under-use of evidenced-based, guideline-recommended chronic HF therapies at hospital discharge. As such, there are substantial opportunities to improve the quality of care for ADHF patients in the nation's hospitals.