Background: Household food insecurity (HFI) can lead to a poor diet and malnutrition. Yet, little is known about the extent to which maternal diet covaries with food insecurity during pregnancy and lactation. Objective: Longitudinal associations between HFI and maternal dietary diversity from early pregnancy to 3mo postpartum were examined in rural Bangladesh. Methods: We repeatedly assessed dietary intake by using a 7-d food-frequency questionnaire in the first and third trimesters of pregnancy and at 3 mo postpartum among 14,600 women enrolled into an antenatal micronutrient supplementation trial. Maternal dietary diversity score (DDS) was constructed as the sumof 10 food groups reportedly consumed at each assessment. Households were classified at 6mo postpartum as being food secure or having mild, moderate, or severe HFI on the basis of a 9-item standard scale. Generalized estimating equations were used to estimate the longitudinal relation between HFI status and DDS and the likelihood of individual food-group consumption, adjusting for confounders at the maternal and household levels. Results: The DDS decreased with progressively worse HFI, an association best explained by a derived household wealth index. Compared with women fromfood-secure households, women of mild, moderate, and severe HFI were less likely, in a dose-response fashion, to have consumed dairy products [adjusted ORs (95% CIs): 0.73 (0.69, 0.78), 0.62 (0.58, 0.66), and 0.52 (0.48, 0.55), respectively], eggs [0.81 (0.76, 0.85), 0.73 (0.68, 0.77), and 0.61 (0.57, 0.65)], meat [0.83 (0.79, 0.88), 0.73 (0.69, 0.78), and 0.60 (0.56, 0.64)], fish [0.87 (0.80, 0.94), 0.76 (0.70, 0.83), and 0.59 (0.54, 0.65)], legumes and nuts [0.88 (0.83, 0.93), 0.81 (0.76, 0.87), and 0.79 (0.74, 0.85)], and yellow and orange fruit and vegetables [0.85 (0.80, 0.91), 0.78 (0.73, 0.84), and 0.72 (0.67, 0.78)]. Neither intakes of dark-green leafy vegetables nor of vegetable oil were associated with HFI status. Conclusion: Antenatal and postnatal maternal dietary diversity, especially intakes of animal-source foods, fruit, and vegetables, declined with worsening food insecurity in rural Bangladesh.