To determine the lifetime and current prevalence, along with other characteristics such as age at onset, patterns of comorbidity, and interest in treatment, of DSM-IV intermittent explosive disorder (IED) in an outpatient psychiatric sample. 1300 individuals presenting for outpatient psychiatric treatment at Rhode Island Hospital, Providence, R.I., underwent structured diagnostic assessment for Axis I and II disorders. The diagnosis of IED was made according to DSM-IV criteria. 6.3% (SE, +/- 0.7%) of patients met criteria for lifetime DSM-IV IED, and 3.1% +/- 0.5% of patients met criteria for current DSM-IV IED. While DSM-IV IED was the current principal diagnosis in only 0.6% +/- 0.2% of patients, most patients with current DSM-IV IED (80%) were interested in treatment for their intermittent aggressive behavior. Only lifetime alcohol/drug disorder was more frequent in DSM-IV IED compared with non-IED patients. Age at onset for DSM-IV IED peaked in the teen years, was earlier for men than women, and occurred earlier than all comorbid disorders, with the exception of phobic anxiety disorders, suggesting that IED cannot be attributed to most comorbid conditions. DSM-IV IED in psychiatric samples is far more common than previously thought. DSM-IV IED develops early in life, especially in male patients, and its development may be independent of most other disorders.