Objective The main objective was to explore early-age conditions associated to Substance Use Disorders (SUD) in adults with Attention Deficit/Hyperactivity Disorder (ADHD); secondly, to determine which of those conditions are specific to ADHD subjects; and finally, to compare ADHD and non-ADHD subjects in terms of SUD lifetime prevalence and professional, social and personal adjustment. Method Comparison between ADHD adults with (n = 236) and without lifetime SUD (n = 309) regarding clinical characteristics of ADHD, externalization disorders, temperamental traits, environmental factors, academic history and family psychiatric history; secondly, ADHD subjects were compared to a non-ADHD group (n = 177) concerning those variables. Results The following variables were found to be positively associated to SUD in ADHD subjects: ADHD severity, CD and ODD comorbidities, temperamental characteristics ("fearful", "accident prone" and "frequent temper tantrums"), "sexual abuse", "be suspended from school", family history of SUD and ADHD, and male gender; ADHD inattentive subtype and "fearful" were inversely associated to SUD. From those variables, "frequent temper tantrums" was also associated to SUD in non-ADHD subjects. ADHD subjects had higher prevalence of lifetime SUD and greater professional, social and personal impairment than non-ADHD subjects. Conclusion Findings suggest a significant association between ADHD, SUD and early-age conditions, such as CD and ODD comorbidity; other variables from childhood, namely, ADHD subtype, temper characteristics ("fearful", "accident prone"), "sexual abuse", "be suspended from school" and family history of ADHD are associated to SUD in ADHD subjects, but not in non-ADHD subjects. Moreover, this study confirms both the higher prevalence of lifetime SUD and greater professional, social and personal impairment in ADHD subjects than in non-ADHD subjects. © 2014 Elsevier Inc.