Because they provide relief of symptoms and reduce mortality, angiotensin-converting enzyme (ACE) inhibitors have become a highly recommended part of the pharmacologic treatment of patients with congestive heart failure (CHF). Although clinical trials suggest that 80% to 90% of patients with CHF tolerate ACE inhibitors, recent surveys reveal that for fewer than this number of patients are actually receiving these drugs. The reasons for this discrepancy are not known. To better understand physician-prescribing behavior, the current study examined the demographic, clinical, laboratory, and medical care characteristics of patients treated and not treated with ACE inhibitors during hospitalization for decompensated CHF. The charts of a consecutive series of patients admitted to 2 acute care hospitals during 1992 (n = 424) were reviewed and comparisons made between those receiving and not receiving ACE inhibitors at the time of hospital admission and hospital discharge. In addition, measures of in-hospital and postdischarge outcome were compared between the groups. The results revealed significant differences in certain demographic variables (e.g., patient age), clinical measures (e.g., left ventricular ejection fraction and serum creatinine), management issues (e.g., documentation of left ventricular function and documentation of etiology of CHF), and treatment strategies (e.g., ancillary drug use). Few differences were noted in measures of severity of CHF (e.g., New York Heart Association functional class and serum sodium level). Death rates were significantly higher for those not receiving ACE inhibitors. Patterns that emerged that could explain under-prescription ACE inhibitors included older age, worse renal function, left ventricular diastolic dysfunction, use of alternate vasodilators, and overall less intense medical management. Programs to educate care providers regarding the proper use of ACE inhibitors in CHF are recommended.