Objective: To explore personality and readiness to change among substance use disorders (SUD) patients with and without ADHD. Method: SUD + ADHD versus SUD – ADHD patients consecutively entering treatment between 2010 and 2012 were compared concerning personality (Temperament and Character Inventory) and readiness to change (Stages of Change Readiness and Treatment Eagerness Scale). Results: Among 103 SUD patients (76 men, age M = 43.3, SD = 11.1), 16 (15.5%) were diagnosed with ADHD. SUD + ADHD patients reported significantly elevated eagerness to effort (p = .008) compared with SUD – ADHD patients, who reported significantly elevated fear of uncertainty (p < .000). SUD + ADHD patients reported higher ambition (p = .025), self-forgetfulness (p = .029), and lower recognition (p = .022). They were younger (p = .019) and showed more often amphetamine addiction (p = .022) compared with SUD – ADHD patients. Conclusion: The distinct characteristics found in SUD + ADHD and SUD – ADHD patients underline the need for differentiated treatment interventions.