Attention deficit hyperactivity disorder (ADHD) appears to share some familial determinants with drug, but not alcohol, dependence. Biederman et al. (CME, p. 107) found that boys with ADHD were more likely than comparison boys to develop drug dependence over 10 years and they had more relatives with drug dependence and with ADHD. Relatives’ risk for drug dependence was higher for boys with ADHD, and relatives’ risk of ADHD was higher for boys with drug dependence. However, risk for alcohol dependence in relatives was seen only in relatives of boys who had both alcohol dependence and ADHD. An editorial on these findings by Dr. Lenard Adler appears on p. 11.