PURPOSE: To assess the extent of off-label prescribing of antiepileptic drugs (AEDs) and associated variables in a large population of patients with pharmacoresistant epilepsy. METHODS: Descriptive analysis of data recorded from consecutively enrolled patients with pharmacoresistant epilepsy attending 11 tertiary referral centers in Italy. Off-label use was stratified by therapeutic indication, dose, and age. Multivariate logistic regression was used to identify variables associated with off-label prescription. RESULTS: Of a total of 1,124 patients enrolled between November 2006 and August 2007, 53 % (101/191) of children and 31 % (287/933) of adults were receiving at least one off-label AED prescription. Among adults, off-label use was related primarily to indication and was highest for clobazam (100 %) and ethosuximide (40 %), followed by lamotrigine (25 %), and vigabatrin (25 %). In children, clobazam (100 %), lamotrigine (79 %), vigabatrin (55 %), ethosuximide (46 %), and levetiracetam (43 %) were most frequently used off-label, with indication or age being the main causes depending on the specific AED. Logistic regression analysis indicated that higher rates of off-label use were associated with a polytherapy regimen (odds ratio [OR] 2.50, 95 % confidence interval [95 % CI], 1.55-4.03), pediatric age (2.49, 1.66-3.76), having failed ≥3 AEDs (2.16, 1.04-4.48), a diagnosis of generalized epilepsy with structural/metabolic or unknown etiology (2.97, 1.25-7.04), and increasing seizure frequency (1.07, 1.01-1.14). CONCLUSIONS: Off-label prescribing of AEDs is common among patients with pharmacoresistant epilepsy and is influenced by demographic and disease-related characteristics. Studies are needed to improve the quality of evidence guiding epilepsy treatment, and to evaluate the risks and benefits of off-label prescribing in epilepsy.