Objective: This 8-week, open-label trial assessed the efficacy of methylphenidate transdermal system (MTS) in 14 adult individuals diagnosed with ADHD and with a history of stimulant misuse, abuse, or dependence. Method: The primary efficacy endpoint was the Wender-Reimherr Adult ADHD Scale (WRAADS), and secondary efficacy endpoints included the Clinical Global Impression (CGI) ratings and substance abuse as quantified by urine drug screens and self-reported use. Results: Significant improvements from baseline were found on both the WRAADS and CGI measurements. No abuse of the study medication was observed. Conclusion: The findings suggested that MTS may improve ADHD symptoms in adults with a history of stimulant misuse; however, there were limitations. The study data showed the need for subsequent randomized studies that further explore findings made in this study. (Contains 3 tables.)