Objective: The main objective of this article is to investigate the type of personality disorders and clinical syndromes (CSs) that were best related to ADHD symptoms among prisoners. Method: The authors screened for childhood and adult ADHD symptoms and administered the Millon Clinical Multiaxial Inventory-III (MCMI-III) to 196 serving prisoners. Results: Childhood and adult ADHD symptoms were most strongly related to the compulsive (negative relationship) and borderline (positive relationship) scales on the MCMI-III with large and medium effect sizes, respectively. Hierarchical multiple regressions revealed that the absence of compulsive personality disorder traits (i.e., a low score as a dimension) was the single best Axis II predictor of childhood and adult ADHD symptoms. CSs did not add significantly to the variance in childhood ADHD beyond that of the personality disorder dimensions, but it did so for current ADHD symptoms in relation to alcohol dependence. Conclusion: The findings demonstrate the relative absence of compulsive personality disorder traits in prisoners with ADHD symptoms as core maladaptive traits involving disorganization. (Contains 4 tables.)