This study examines differences in outpatient-visit frequency and medical expenditures between (1) children and adolescents in Taiwan with intellectual disabilities and (2) children and adolescents in Taiwan's general population. A cross-sectional study was conducted to analyze data from 2007 provided by Taiwan's National Health Insurance program. A total of 236,045 beneficiaries younger than 19 years made use of outpatient services; among them, 35,802 had a principal diagnosis of mental retardation (intellectual disability). The average number of ambulatory visits was 14.9 ± 12.4, which is much higher than in the United States and other developed countries. The mean number of annual visits of the individuals with intellectual disabilities was significantly higher than that of the general population in Taiwan (20.1 ± 20.0 vs. 14.0 ± 12.2); age, gender, urbanization level of residential area, and copayment status affected outpatient visit frequency. The mean annual outpatient costs were NTD6371.3 ± NTD11989.1 for the general population and NTD19724.9 ± NTD40469.9 for those with intellectual disabilities (US $1 equals approximately NTD30). Age, gender, urbanization level of residential area, and copayment status were the determinants that accounted for this difference in cost. Children and adolescents with intellectual disabilities had higher use rates of rehabilitative and psychiatric services than the general population. We conclude that individuals with intellectual disabilities had higher demands than the general population for healthcare services, especially for rehabilitative and psychiatric services.