In psychiatry, adjustment disorder (AD) is a psychological response to an identifiable stressor or group of stressors that cause(s) significant emotional or behavioral symptoms that do not meet criteria for anxiety disorder, PTSD, or acute stress disorder. The condition is different from anxiety disorder, which lacks the presence of a stressor, or post-traumatic stress disorder and acute stress disorder, which usually are associated with a more intense stressor. There are nine different types of adjustment disorders listed in the DSM-III-R. In DSM-IV, adjustment disorder was reduced to six types, classified by their clinical features. Adjustment disorder may also be acute or chronic, depending on whether it lasts more or less than six months. Diagnosis of adjustment disorder is quite common; there is an estimated incidence of 5-21% among psychiatric consultation services for adults. Adult women are diagnosed twice as often as are adult men, but among children and adolescents, girls and boys are equally likely to receive this diagnosis. Adjustment disorder was introduced into the psychiatric classification systems almost 30 years ago, but the concept was recognized for many years before that.