Few studies have examined the association between body mass index (BMI: kg/m(2)) and pancreatic cancer risk in Asian populations. We examined this relationship in 51,251 Chinese men and women aged 45-74 who enrolled between 1993 and 1998 in the population based, prospective Singapore Chinese Health Study. Data were collected through in-person interviews. By December 31, 2011, 194 cohort participants had developed pancreatic cancer. A Cox proportional hazards model was used to estimate hazard ratios (HR) and their 95% confidence intervals (95% CI). We hypothesized the association between BMI and pancreatic cancer risk may vary by smoking status (ever v. never) and there was evidence for this as the interaction between BMI and smoking status was significant (p = 0.018). Among ever smokers, being classified as underweight (BMI <18.5 kg/m(2)), was associated with a significantly elevated risk of pancreatic cancer relative to smokers with a BMI of 21.5-24.4 kg/m(2) (HR = 1.99, 95% CI = 1.03-3.84). This association was strengthened after exclusion of the first three years of follow-up time. Among never smokers, there was no association between BMI and pancreatic cancer risk. However, after excluding pancreatic cancer cases and person-years in the first three years of follow-up, never smokers with a BMI ≥ 27.5 kg/m(2) showed a suggestive increased risk of pancreatic cancer relative to never smokers with a BMI of 21.5-24.4 kg/m(2) (HR = 1.75, 95% CI = 0.93-3.3). In conclusion, Singaporean Chinese who were underweight with a history of smoking had an increased risk of developing pancreatic cancer, whereas there was no significant association between BMI and pancreatic cancer in never smokers.