Objective: To quantify factors influencing iron supplementation compliance and haemoglobin (Hb) concentrations among pregnant women participating in an iron supplementation programme under routine field conditions. Design: Cross-sectional interviews and Hb measurements. Settings: Albay and Sorsogon provinces, Bicol, Philippines. Subjects: Three hundred and forty-six pregnant women receiving iron supplements via the Philippine iron supplementation programme. Results: Women had a mean Hb concentration of 10.756 1.43 g dl 21, and 56.4% were anaemic (Hb , 11.0 g dl 21). On average, the first prenatal visit occurred at nearly 4 months (3.806 1.56). The ratio of visits to number of months pregnant was 0.51 6 0.24. Self-reported consumption of pills received was 85% (0.856 0.23), although pill counts suggested that consumption was 70% (0.706 0.35). Using multiple regression, an earlier first prenatal visit and greater self-reported compliance were positively associated with Hb concentrations. Additionally, perceived health benefits from taking the supplements and higher health programme knowledge were positively associated with pill consumption, while experiencing side-effects and disliking the taste of the supplements were associated with lower pill consumption. A greater number of living children was negatively associated with the frequency of prenatal visits. The number of children was also directly negatively associated with Hb concentrations. Conclusions: Compliance was positively related to Hb concentrations. Several factors associated with greater compliance were identified, including marital status, number of children, health programme knowledge, side-effects, perceived health benefits, and dislike of taste. Some of these factors may serve as avenues for interventions to increase compliance, and ultimately Hb concentrations