Objective: Given the paucity of research among prisoners, this study aimed to examine the prevalence and psychiatric comorbidity associated with adult ADHD. Method: The study was conducted at four NSW correctional facilities (2 male; 2 female). Results: Thirty-five percent of the sample screened positive for adult ADHD, and 17% of the sample met criteria for a full diagnosis. After adjustment, benzodiazepine dependence, borderline personality disorder, social phobia, antisocial personality disorder, and a number of lifetime psychological disorders remained significantly and independently associated with the diagnosis of adult ADHD. Lowering the threshold on the ADHD Self-Rating Scale to 3 (vs. 4) increased the sensitivity (80%-93%), but lowered the specificity (55%-47%). Conclusion: Adult ADHD among NSW prisoners is elevated, with substance use disorders and psychiatric comorbidity common. A greater acceptance of this disorder among prisoners, and appropriate treatment, is warranted.