Attention deficit hyperactivity disorder is one of the most common neuropsychiatric disorders in childhood. Electroencephalographic abnormalities may be observed but it is controversial to perform electroencephalography before starting the treatment. Awake electroencephalography findings, demographic and psychometric variables of patients with attention deficit hyperactivity disorder treated between January 2005 and December 2010 were retrospectively evaluated. The study included 386 patients aged 4-18 (mean 9.61±3.04) years, who were diagnosed with attention deficit hyperactivity disorder according to the DSM-IV-TR (2000) diagnostic criteria. Epileptiform electroencephalography pattern was observed in 22/386 (5.7%) patients. Seven of 386 (1.8%) patients had a history of epilepsy diagnosis and antiepileptic medication. When patients with seizure history (with or without epilepsy diagnosis) and those with epileptic abnormalities on electroencephalography were excluded, the incidence of epileptiform abnormalities in attention deficit hyperactivity disorder patients was 12/386 (3.1%). After psychostimulant medication, epileptic seizures occurred in only three patients with epilepsy. The prevalence rate of epileptiform discharges on awake electroencephalography, observed in attention deficit hyperactivity disorder patients before psychostimulant treatment is similar to that in healthy schoolchildren. Since the seizures increased only in epileptic patients, we do not recommend routine awake electroencephalography evaluation in children with attention deficit hyperactivity disorder before psychostimulant medication.