OBJECTIVE: To determine if certain diagnoses and comorbidities influence the risk of hospitalization for angina patients. METHODS: Study was conducted using IMS HEALTH's LifeLink(tm) database, a U.S. employer claims database consisting of more than 1.8 million covered lives, with linked medical and pharmacy claims for employees, dependents, and retirees from 1991 forward. Patients were diagnosed with angina in the period 3/1/99 - 2/29/00. Unstable angina patients were placed in a single cohort. Stable angina patients were further classified based on the presence of hypertension, congestive heart failure (CHF), diabetes, or other heart disease in the 36 months preceding their angina diagnosis. RESULTS: 125,453 patients met the inclusion criteria - 32,672 with unstable angina and 92,781 with stable angina. Patients with unstable angina were significantly more likely to be hospitalized (53.3%) than patients with stable angina (27.3%) (p<0.001). When comparing unstable to stable angina patients with comorbid conditions, patients with unstable angina were more likely to be hospitalized than stable angina patients, regardless of the combination of comorbidities in stable angina patients (odds ratios between 1.20 and 10.47). Stable angina patients with comorbid hypertension, diabetes, and CHF had the most similar risk of hospitalization compared to unstable angina patients, but still were significantly less likely to be hospitalized (OR=0.83, 95% CI=0.79, 0.87). Unstable angina patients had the highest likelihood of hospitalization compared to patients with stable angina and no comorbidities (OR=10.47, 95% CI=9.76, 11.22). Among stable angina patients, hospitalization rates were highest for patients with comorbid CHF (ranging from 36.6% for patients with CHF only to 48.7% for patients with CHF, hypertension, and diabetes). CONCLUSIONS: Patients with unstable angina were significantly more likely than stable angina patients to be hospitalized, even if the stable angina patients had a number of complicating comorbid conditions. Presence of unstable angina greatly increased the risk of hospitalization.