Childhood asthma is a major public health problem in the United States, particularly among minority populations. The aim of our study was to examine the relationship among ethnicity, allergen sensitization, spirometric measures, and asthma severity in children with mild to severe asthma who received their medical care in Hartford, Connecticut. Four hundred thirty-eight children aged 4-18 years who were enrolled in an asthma care program (Easy Breathing) in Hartford and who were referred for spirometry and allergy skin testing participated in this cross-sectional study. Risk factors for increased asthma severity as defined by National Asthma Education and Prevention Program (NAEPP) guidelines were determined using multinomial logistic regression. Of 438 children, 383 (87.4%) had mild to moderate asthma, and 292 (66.7%) had at least one positive skin test to allergens. Forced expiratory volume in 1 sec/forced vital capacity (FEV1/FVC) was significantly decreased in children with severe vs. mild asthma (80.7 vs. 87.3, respectively). In a multivariate analysis, predictors of severe asthma included African-American ethnicity (odds ratio (OR)=3.70, 95% confidence interval (CI)=1.10-12.42), Puerto Rican ethnicity (OR=3.55, 95% CI=1.18-10.67), sensitization to cockroach allergen (OR=4.34, 95% CI=1.73-10.86), and decreased FEV1/FVC (OR for every 1% decrease in FEV1/FVC=1.06, 95% CI=1.02-1.11). In conclusion, among children with asthma in Hartford and its surrounding communities, predictors of disease severity included African-American ethnicity, Puerto Rican ethnicity, sensitization to cockroach allergen, and decreased FEV1/FVC. Our findings suggest that FEV1/FVC is a useful indicator of asthma severity in children.