Patients with schizophrenia and with ADHD smoke cigarettes at a higher rate than normal subjects (Borland and Heckman 1976). Forty-two percent of men and 38% of women diagnosed with ADHD are current smokers, almost twice as high as the number in an unselected population (Milberger et al. 1997; Pomerleau et al. 1995). In this study we hypothesized that the allele 113bp in D15S1360 marker at CHRNA7 and the 2bp deletion allele at CHRFAM7A are associated with increased smoking in patients with schizophrenia and Adult ADHD. Our sample consisted of 78 DSM-IV patients affected by Adult ADHD and schizophrenia from the Toronto area. Current smoking status was assessed by a medical history questionnaire, and there were 29 current smokers and 49 non-smokers. We analyze the single marker association by chi-square and the CHRNA7-CHRFAM7A interaction by logistic regression, considering the 113bp and the –2bp deletion dominant. In our sample the 113bp allele in CHRNA7 does not confer risk for smoking in the ADHD (chi-sq=0.47, 1df, p=0.492). Finally, we compared the frequency of the 133bp genotype in schizophrenic smokers with non psychiatric smokers who started nicotine replacement treatment and we found significant difference in genotype distribution (p=0.0063). The analysis of a7 genes in ADHD showed no association with smoking. The molecular hypothesis of a7/a7like interaction and the number of a7like copy variation remains very interesting for psychiatric phenotype and nicotine addiction even though the a7/a7like showed no interaction in conferring risk for smoking in this sample.