PURPOSE: The effects of orally administered midazolam on three groups of preschool children who differed by age only and required dental treatment were studied. Sixty-one children age 24-58 months participated in this institutionally-approved study. METHODS: Selection criteria for the children included: demonstrated disruptive behaviors; healthy (ASA I); required at least one restorative appointment involving a posterior quadrant; no known drug allergies; were between two and five years of age; and had no prior experience with sedative trials. The children were divided into three groups according to age: Group I (24-35 months), Group II (36-47 months), and Group III (47-59 months). Each child received midazolam 0.5 mg/kg orally 15 minutes before treatment. Behavior was evaluated using the Ohio State Behavior Rating Scale (OS). Physiological parameters including heart rate, oxygen saturation, systolic and diastolic blood pressure were also evaluated. Data were analyzed using chi-square, cross tabulation, descriptive statistics, ANOVA, t-tests, and regression and correlation analysis. RESULTS: Results indicated no statistically significant difference in behavior across all age groups as evaluated by the OS. CONCLUSION: No significant differences of clinical significance were noted.