OBJECTIVE: To determine factors associated with ruptured appendicitis among children, using administrative databases. Insurance-related differences in the risk of ruptured appendix among adults in California have previously been described (Braveman, Schaaf, Egerter, et al. 1994). DATA SOURCES/STUDY SETTING: State of Maryland Medicaid claims data for children < or = 18 years of age from 1989 to 1993 and hospital discharge data for children < or = 19 years of age from 1989 to 1994 were analyzed. STUDY DESIGN: Administrative data analysis pre- and post-implementation of a Medicaid managed care program called Maryland Access to Care. DATA COLLECTION/EXTRACTION METHODS: Medicaid claims and hospital discharge ICD-9-CM codes were used to define hospitalization for ruptured and nonruptured appendicitis. Linear regression was used to model trends. Logistic regression was used to model the probability of ruptured appendicitis. PRINCIPAL FINDINGS: Among the 374 Medicaid inpatient claims for appendicitis, 37 percent were for ruptured appendicitis. Among the 5,141 hospital discharges for appendicitis, 30 percent were for ruptured appendicitis. Using Medicaid claims data, the probability of ruptured appendicitis was inversely related to age (OR = 0.86, 95% CI 0.81-0.91), white race (OR = 0.35, 95% CI 0.17-0.71) and preventive care visits (OR = 0.19, 95% CI 0.05-0.77). Using hospital discharge data, age (OR = 0.91, 95% CI 0.90-0.93) and female gender (OR = 0.87, 95% CI 0.77-0.99) were significant covariates. Insurance-related covariates were not significant in multivariate models addressing the probability of ruptured appendicitis. CONCLUSIONS: During a period of rapid managed care growth, insurance type was not associated with an increased risk of ruptured appendicitis among children in this geographic area. Age, female gender, and the number of preventive care visits are inversely related to the risk of ruptured appendix among children. The protective effect of preventive care visits suggests that a primary care relationship facilitates access to care, thus reducing delay in the management of appendicitis.