This study examined healthcare services used by children with attention-deficit/hyperactivity disorder (ADHD), with and without psychiatric comorbidities. The study was conducted in a large health maintenance organization in the Pacific Northwest on all continuously enrolled children aged 5 to 12 from January 1997 through July 1998. The study measured all outpatient medical care, specialty mental health care services, and prescription drug dispensings from computer records. Children with ADHD, with and without other psychiatric comorbidities, use more general medical services than do other groups of children, including outpatient visits, acute care (emergency room [ER] urgent care) visits. ADHD and other psychiatric comorbidities lead to higher use of specialty mental health services and greater use of psychotropic medications.