Objective: The objective of this study was to compare psychiatric comorbidity and consumption-related variables in ADHD patients seeking treatment for cocaine, cannabis, or both. Method: Assessment was conducted using European Addiction Severity Index (EuropASI), Conners’ Adult ADHD Diagnostic Interview (CAADID), Structured Clinical Interview for DSM Disorders (SCID), Adult Self-Report Scale (ASRS), Wender Utah Rating Scale (WURS), Barratt Impulsiveness Scale-11 (BIS-11), and FIDI, with statistical analyses of analysis of variance (ANOVA), Student’s t test, chi-square test, and multinomial regression model. Results: In total, 1,538 patients with substance use disorder (SUD) were evaluated for ADHD; 239 (15.5%) had ADHD, with cannabis 41, cannabis/cocaine 36, and cocaine 74. Men represented 80%, with mean age of 32.9 ± 10 years. Significant variables were—in bivariate analysis—more years of cannabis use in cannabis group and younger age for cocaine use disorder in cannabis/cocaine group, and—in multivariate analysis—lifetime anxiety disorder and younger age at onset of any SUD in cannabis group and working affected scale in cannabis and polysubstance use in cannabis/cocaine group. Conclusion: Groups with cannabis use had higher severity. ADHD features were similar in all groups. The assessment of ADHD and comorbid disorders is important.