OBJECTIVES: To determine if switching from select branded to generic equivalent antiepileptic drug (AED) in patients with epilepsy is associated with adverse outcomes or with utilization changes that may proxy for adverse outcomes. METHODS: A retrospective cohort study using a large health insurance plan claims database was undertaken comparing patients with ICD-9-CM codes of epilepsy or non-febrile convulsions who switched from brand to generic equivalent AED after 6 months (switch cohort) to those who remained on the brand (non-switch cohort). Potential non-switch subjects were matched 1:1 to 745 phenytoin switch patients, 995 lamotrigine switch patients and 399 divalproex switch patients. Outcomes measured included the event rate ratio (ERR) of the composite of all-cause emergency department (ED) visits or hospitalizations and the incidence rate ratio (IRR) of discontinuation of the index AED, change in dose of index AED or addition of another AED. RESULTS: The switch vs. non-switch cohorts did not demonstrate differences in ED visits or hospitalizations for the studied AEDs (ERR for phenytoin 0.96, 95% CI 0.80 – 1.16; ERR for lamotrigine 0.97, 95% CI 0.80-1.17; ERR for divalproex 0.83, 95% CI 0.66 – 1.06). Compared with non-switchers, the phenytoin switch cohort had greater incidence of AED utilization changes (IRR 1.85, 95% CI 1.50 – 2.29). Lamotrigine and divalproex showed no differences in AED utilization between the switchers and non-switchers (IRR for lamotrigine 1.00, 95% CI 0.84 – 1.19; IRR for divalproex 1.02, 95% CI, 0.88 – 1.42). CONCLUSIONS: Lamotrigine or divalproex brand to generic switching was not associated with increased incidence of ED visits or hospitalizations or utilization changes compared with patients remaining on the branded product. Brand to generic switching of phenytoin was not associated with an increase in ED visits or hospitalizations but was associated with greater numbers of index drug discontinuations, dose changes or therapy augmentations.