Objective: Estimate rates of medical and psychiatric comorbidity in patients with seizures. Background Rates of incidence and prevalence of epilepsy across populations and countries have proven reasonably consistent across studies that now reach back over decades of inquiry; rates of psychiatric and medical comorbidity have received only more recent directed attention. As part of a collaborative study of the Institute of Medicine9s Committee on the Public Health Dimensions of the Epilepsies, we sought to assess comorbidity rates in the Geisinger Health System (GHS). Design/Methods: Data were retrieved from GHS9s electronic Clinical Decision Intelligence System (CDIS), into which data are entered automatically on an ongoing basis from the electronic medical record system, EpicCare. Prevalent diagnosis of epilepsy was defined as appearance of two codes: either 1. two separate outpatient care visits with epilepsy-related ICD-9-CM code (any diagnosis 345.__, or 780.09 Alteration of Awareness NOS, or 780.39 Convulsive Disorder NOS), or 2. any one of these codes AND one outpatient anticonvulsant medication order. Incident epilepsy was defined as meeting the prevalent definition in a file with no such codes entered for full two year period of primary care established within the system. Results:Prevalence: 10.2 cases per 1000 patients.Incidence: 20.8 per 100,000 patient years.Rates by diagnosis: Incident Epilepsy N=486, Prevalent Epilepsy N=4293, Non-Epileptic Primary Care Population N=416,881Mental Health (One Dx): 86.2%, 69.3%, 32.5%Mental Health (>1 Dx): 47.3%, 58.7%, 24.0%Cerebral Palsy: 2.7%, 5.5%, 0.1%Cerebrovascular disease: 4.7%, 3.2%, 0.7%Dementia: 1.9%, 2.0%, 0.4%Parkinson9s Disease: 1.2%, 1.1%, 0.3%Multiple Sclerosis: 0.8%, 0.8%, 0.2%Traumatic Brain Injury: 1.9%, 3.1%, 0.4%Autism: 1.2%, 1.7%, 0.1%Ischemic Heart Disease: 5.1%, 8.0%, 4.1%Asthma: 13.0%,13.0%, 6.9%Obesity: 8.2%, 9.1%, 1.6%Morbid Obesity: 2.7%, 3.1%, 1.6%Cancer: 6.2%, 9.8%, 4.7%Obstructive Sleep Apnea: 0.4%, 1.8%, 0.7% Conclusions: Psychiatric diagnoses especially, and many other medical diagnoses, are of much higher prevalence in patients with seizure disorders than in a general primary care population. Disclosure: Dr. Eccher has nothing to disclose. Dr. Bengier has nothing to disclose. Dr. Liberman has received personal compensation for activities with CVS Caremark and Geisinger as an employee.