A cross-sectional prevalence study of anemia was undertaken on 412 pregnant women in northeast Thailand during January 2003 to May 2004. With standardized diagnostic protocols and the CDC criteria of anemia [hemoglobin (Hb) < 11 g/dl at < or = 12 weeks of gestation and Hb < 10.5 g/dl at < or = 20 weeks of gestation], 71 (17.2%) subjects were anemic. Of these, 42 (59.2%) subjects had thalassemia, 5 (7.0%) had iron deficiency, 18 (25.4%) had combined thalassemia and iron deficiency and 6 (8.5%) had no thalassemia nor iron deficiency. Adjusted logistic regression analyses indicated that various thalassemia genotypes were significantly related to anemia, while homozygous Hb E had the highest risk with an odds ratio (OR) of 44.8 (95% CI 12.6-159.7). In comparison, iron deficiency demonstrated a much lower risk with OR of 3.1 (95% CI 1.4-6.8). This finding suggests that the contribution of iron deficiency to pregnancy associated anemia in this region is low.