This study was conducted to explore the association between attempted suicides and body mass index (BMI, kg/m2) in a family sample of 2547 individuals. As a comparison, a national NESARC (the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions) sample of 41 589 individuals was included to validate the observed association. Compared to average weight, extreme obesity showed significantly increased odds for attempted suicides both in family sample (odds ratio (OR) = 3.37 and 95% confidence interval (CI) = 1.59-7.13 for BMI = 40- < 50 kg/m2; OR = 3.85 and 95% CI = 1.71-8.66 for BMI > or = 50 kg/m2) and in NESARC sample (OR = 2.11 and 95% CI = 1.59-2.81 for BMI = 40- < 50 kg/m2; OR = 2.56 and 95% CI = 1.34-4.92 for BMI> or = 50 kg/m2) after adjustment for sociodemographic factors. Compared to general population, the risk for attempted suicide was 87 and 122% higher for those with BMI=40- < 50 and > or = 50 kg/m2, respectively. The pattern of results in the family and population studies indicates that extreme obesity is strongly associated with attempted suicide.