The prevalence of ADHD in patients with Substance Use Disorder (SUD) is high, with an average of 14%, depending on the frequencies, with the DSM-5 criteria can vary by 9-33%, depending on the country and the diagnostic methods used, much higher figures compared to the presence of ADHD in the general population 1-7.3% (Crunelle, Van Den Brink, et al., 2018; van de Glind, et al., 2014; Van Emmerik-van Oortmerssen et al., 2014). Both the SUD and ADHD, as well as other psychiatric comorbidities very prevalent in this group, are important in the diagnostic process. The objective of this study is to evaluate differences in psychiatric comorbidity and severity of addiction between patients with ADHD and TUS, as well as their evolution. The evolution assessment was based on two variables: abstinence from the substance that was the reason for consultation and the time of follow-up in the outpatient treatment center. Methods: Two studies have been carried out, a first 6-month follow-up study in which the variables of psychiatric comorbidity, severity of consumption, abstinence and follow-up time in an outpatient treatment were evaluated, depending on the presence or not of ADHD. A second study assessed the severity of addiction, ADHD and psychiatric comorbidity in patients diagnosed with ADHD and with cannabis, cocaine or cannabis / cocaine use disorder. Semi-structured questionnaires and interviews will be used to measure the variables, among these are: EuropASI, CAADID, SCID-I and SCID-II; and ASRS, WURS, BIS-11 and FIDI questionnaires were evaluated. Statistical analysis was performed for single and multiple variables, comparison of two or more of two groups (Chi square, Man Whitney U, t-student), as well as multivariate linear regression analysis; for the assessment of evolution, the Kaplan-Meyer survival analysis was considered. Results: Study 1: A total of 406 patients were evaluated in a follow up periedo on 1, 3 and 6 months. The ADHD group reported youngest age, cannabis as the most commonly used drug, earlier age for the beginning of problematic substance use, more prevalence of personality disorders of both cluster A and cluster B, as well as more presence of conduct disorder in childhood. The ADHD group presented less abstinence time and less months of retention or follow-up time in outpatient treatment. ADHD was associated with greater impulsivity at all scales, mainly those related to dysfunctional impulsivity. In study 2, a total of 1538 patients were evaluated, of which 239 fullfielld criteria for ADHD diagnosis; the mean age was 32.9 ± 10 years, mainly men. The combined presentation of ADHD was the most frequent (64.2%). Anxiety disorder throughout life, work skills, consumption of polysubstances and the evolution of substance use throughout life were variables with statistic significance in the multivariate analysis when were compared the groups of patients (cannabis, cannabis / cocaine and cocaine SUD). The most affected groups were those with cannabis use as a common factor. It is concluded that patients with ADHD and SUD, have more seriousness in terms of consumption, more prevalence of psychiatric comorbidity, less abstinence time and less retention in an outpatient treatment; the drug of consumption identified as more prevalent in this group is cannabis. The significant variables in both studies were: Earlier age at start of drug consumption or dependence, worst punctuation on the drug scale in the EuropASI, earlier relapse in consumption and in drop out for ambulatory drug treatment, more prevalence of psychiatric comorbidity; all of these variables inferred high risk for present more severity and worse prognosis in patients with SUD and ADHD. The diagnosis and comprehensive therapeutic approach of SUD and ADHD patients as well as other psychiatric comorbidities is important.