Objective: To examine ADHD prevalence, rating scales, and relationship to nicotine use in adults with schizophrenia or Asperger syndrome. Method: Ninety-five individuals, 41 with schizophrenia and 54 with Asperger syndrome, were included. Self-rating of adult ADHD symptoms with the Wender–Reimherr Adult Attention Deficit Diagnostic Rating Scale (WRAADDS), parent rating of proband’s ADHD childhood and adult life symptoms using the Swanson, Nolan, and Pelham Questionnaire (SNAP), and report of clinical ADHD diagnosis were included as ADHD measures. Nicotine use data were compared with data from a population sample. Results: In all, 10% of the schizophrenia group and 30% of the Asperger syndrome group had a clinical ADHD diagnosis. Nicotine dependency in the whole sample was closely linked to ADHD. Conclusion: The prevalence of comorbid ADHD was high in schizophrenia and Asperger syndrome. The WRAADDS self-rating scale for ADHD can be one useful tool for assessing comorbid ADHD in these patient groups. (J. of Att. Dis. 2012; XX(X) 1-XX)