OBJECTIVE: To examine the prevalence of smoking behaviors among adults with diabetes on the United States-Mexico border, to compare these behaviors in U.S. Hispanics and Mexicans with diabetes, and to identify explanations for group differences. METHODS: Data came from the U.S.-Mexico Border Diabetes Prevention and Control Project survey (2001-2002), a stratified, multistage sample representative of the border population. The analytic sample included adults from all racial and ethnic backgrounds with diabetes (n = 665), including 333 Mexicans and 268 U.S. Hispanics. Smoking behaviors were based on self-reports. Age- and gender-specific prevalence of smoking behavior was estimated and logistic regression was used for mediation analysis of group differences. RESULTS: One in five adults with diabetes (20.1%) in the region was a current smoker. Prevalence was higher among Mexicans (26.2%) than U.S. Hispanics (10.1%, P = 0.003); differences were not explained by sociodemographic or healthcare-related characteristics (odds ratio [OR] 3.86, 95% confidence interval [CI] 1.50-9.91, P = 0.004). Younger Mexicans with diabetes (< 55 years) were four times more likely to smoke than younger U.S. Hispanics (32.1% versus 8.1%, P < 0.001) and Mexican men with diabetes were more than twice as likely to smoke as U.S. Hispanic men (38.9% versus 15.8%, P = 0.003). Among adults with diabetes with a smoking history, 52.5% were former smokers; U.S. Hispanics were more likely to be former smokers than Mexicans with diabetes (62.6% versus 27.5%, P = 0.001). A marginally significant difference remained after adjusting for potential mediators (OR 0.42, 95% CI 0.17-1.08, P = 0.074). CONCLUSIONES: Smoking interventions should focus on Mexicans with diabetes in the border region, especially younger adults and men. Identifying sources of differences in smoking behaviors among border groups with diabetes may further inform intervention.