Background: There has been no longitudinal study in Taiwan to identify the nature and the scale of medical care utilization of people with intellectual disabilities (IDs) up to the present. The aim of this study is to describe inpatient utilization among people under ID care in institutions in order to identify the pattern of medical care needs and the factors affecting utilization in Taiwan. Method: The subject cohort was 168 individuals with ID who were cared for by a large public disability institution from 1999 to 2002 in Taipei, Taiwan. Results: On the examination of the inpatient care that these persons underwent, it was found that these individuals had a heightened need (inpatient rate: 10.1-14.9) for inpatient care compared with the general population with disabilities (9.37%) in Taiwan. The main reasons for hospitalization were pneumonia, gastrointestinal disorders, cellulites, orthopaedic problems, epilepsy and bronchitis. Using the full model of Generalized Estimating Equations for inpatient care utilization, the factors including low income family, living in an institution, being a subject with cerebral palsy and being a high outpatient user all influenced the use of inpatient care. Conclusions: This study highlights that health authorities need to promote health planning more in order to ensure an excellent quality of health monitoring and health promotion among people with ID cared for by institutions.