ARTICLE ABSTRACTBackground: A history of diabetes is associated with an increased risk of several types of cancers. Whether diabetes is a risk factor for head and neck cancer (HNC) has received little attention.Methods: We pooled data from 12 case–control studies including 6,448 cases and 13,747 controls, and estimated OR and 95% CI for the associations between diabetes and HNC, adjusted for age, education level, sex, race/ethnicity, study center, cigarette smoking, alcohol use, and body mass index.Results: We observed a weak association between diabetes and the incidence of HNC overall (OR, 1.09; 95% CI: 0.95–1.24). However, we observed a modest association among never smokers (OR, 1.59; 95% CI: 1.22–2.07), and no association among ever smokers (OR, 0.96; 95% CI: 0.83–1.11); likelihood ratio test for interaction P = 0.001.Conclusion: A history of diabetes was weakly associated with HNC overall, but we observed evidence of effect modification by smoking status, with a positive association among those who never smoked cigarettes.Impact: This study suggests that glucose metabolism abnormalities may be a HNC risk factor in subgroups of the population. Prospective studies incorporating biomarkers are needed to improve our understanding of the relationship between diabetes and HNC risk, possibly providing new strategies in the prevention of HNC. Cancer Epidemiol Biomarkers Prev; 21(2); 294–304. ©2011 AACR.