OBJECTIVE: To examine a medical records database to determine the prevalence of insomnia in patients with a history of drug dependence or abuse. METHODS: Data from April, 1996 to September, 2003 on patients with a diagnosis of drug dependence or abuse (ICD-9 code 303.9, 304-305 [except tobacco use, 305.1]) were extracted from the GE Medical Systems database – a large outpatient database with input from over 2000 practicing physicians. The insomnia cohort was defined as patients having either a diagnosis consistent with insomnia (ICD-9 codes 307.4x [x=1-2, 9] and 780.5x [x=0,2]) or a prescription for insomnia medication. Demographic characteristics, comorbid conditions, and concomitant medications were evaluated. RESULTS: A total of 13,861 patients in the database constituted the population with drug dependence or abuse, and 2,479 (17.9%) of these composed the insomnia cohort. This insomnia prevalence rate was more than twice that in the population without reported drug abuse or dependence (7.4%; 115,487 of 1,567,751). Alcohol abuse was the most prevalent type of drug dependence or abuse diagnosed in the insomnia cohort. The most frequently reported comorbidities were depressive disorders (32.4%), neurotic disorders (28.6%), and other unspecified disorders of the back (23.4%). Analgesics (70.3%), psychotherapeutics (81.1%), and anti-infective agents (61.4%) were among the most common concomitant medications. CONCLUSIONS: Patients with drug dependence or abuse were more than twice as likely to have a diagnosis or prescription for insomnia medication compared with patients without drug dependence or abuse. The insomnia cohort had a high rate of comorbidities and prescriptions for concomitant medications. These data suggest that insomnia is a common comorbid problem in patients with diagnosed histories of drug dependence or abuse. Since this specific population has unique issues and concerns related to use of prescription sedative hypnotic medications, further studies examining safe, nonaddicting, and effective therapies for comorbid insomnia should be pursued.