Understanding factors associated with process measure nonadherence may improve both patient care and future measure design.We analyzed 3401 patients with heart failure and 2186 patients with pneumonia who were eligible for at least 1 National Hospital Quality Measure at an urban tertiary medical center from July 1, 2004, to June 30, 2008. We investigated the association of socioeconomic, demographic, clinical, and care delivery factors with process measure nonadherence, using multivariable analysis.Demographic and socioeconomic variables were unrelated to heart failure measure adherence. Nonadherence with angiotensin-converting enzyme inhibitor/angiotensin II receptor blocker use was more common in patients with renal failure (odds ratio [OR] 2.56; 95% confidence interval [CI], 1.46-4.49), and patients admitted to noncardiac units more often failed the heart failure all-or-none measure (OR 2.22; 95% CI, 1.79-2.75). Patients with pneumonia who were admitted via the emergency department were less likely to fail antibiotic timing (OR 0.41; 95% CI, 0.27-0.63), whereas those with a history of methicillin-resistant Staphylococcus aureus (OR 2.63; 95% CI, 1.31-5.28) or requiring intensive care unit admission (OR 11.4; 95% CI, 6.3-20.8) were more likely to fail the antibiotic selection measure.Demographic and socioeconomic factors were generally unrelated to process measure nonadherence, demonstrating that excellent inpatient care can be delivered even to vulnerable populations. Clinical predictors suggest opportunities for improving both medical record documentation of appropriate exclusions and future measure specifications, especially for complex patients. Care delivery factors substantially affect process adherence.