Objectives To analyze the prevalence of poor oral health and selected determinants in First Nations (FN) and Caucasian samples in Manitoba, Canada. Study design Cross-sectional survey, nested in a cohort study. Methods FN and Caucasian participants completed a questionnaire on socio-demographic variables, oral health symptoms, and oral health-related behaviours as part of a broader cohort study comparing these ethnic groups for different chronic immune mediated diseases. Results Caucasians reported higher levels of employment, education, and urban dwelling than FNs (p<0.001). FNs reported smoking more, and having poorer oral health-related behaviours than Caucasians (p<0.001). After adjustment for age and sex, FN reported having more oral health symptoms than Caucasians (odds ratio (OR): 2.71; 95% confidence interval (CI): 1.73, 4.52), but the association was reduced and not statistically significant after adjustment for other socio-demographic variables (OR=1.34; 95% CI: 0.58, 3.10). Oral health symptoms were associated with current smoking among FN (adjusted OR=2.67, 95% CI: 1.05, 6.78). Oral hygiene behaviours were significantly related to smoking status, rural living and education for both groups. Conclusions Oral health-related behaviours and smoking were found to be significant factors explaining poor oral health, which were lower for the FNs cohort than the Caucasian sample. However oral health and related behaviours were less related to their ethnicity than to socio-demographic factors, suggesting that policies to change behaviour will not result in lasting reductions in oral health differences between these groups in Manitoba.