In this controlled study we evaluated the frequency of psychiatric disorders (PDs) in 100 patients with juvenile myoclonic epilepsy (JME) and compared it with that of 100 healthy controls matched with respect to age, gender, schooling, and socioeconomic status. Our aim was to quantify the frequency of PDs and evaluate the relationship between PDs and factors related to epilepsy. Subjects were evaluated with the Structured Clinical Interview for DSM-IV Axis I disorders (SCID-I) and Axis II disorders (SCID-II). Patients with JME presented with significantly more PDs (P<0.01) and psychosocial problems (P<0.01) than the controls. PDs were diagnosed in 49 patients with JME. Anxiety and mood disorders, present in 23 and 19 patients, respectively, were the most frequently observed. Twenty patients fulfilled criteria for personality disorders; 17 (85%) patients had cluster B personalities comprising the behavioral characteristics impulsivity, humor reactivity, emotional instability, and difficulty in accepting social rules, similar to those cited in the earliest mentioned description of this syndrome. PDs were more frequently observed in patients with higher seizure frequency (P<0.05).