BACKGROUND: Limited research exists on interest in and use of smoking cessation support in pregnancy and postpartum. METHODS: A longitudinal cohort of pregnant smokers and recent ex-smokers were recruited in Nottinghamshire, United Kingdom (N = 850). Data were collected at 8-26 weeks gestation, 34-36 weeks gestation, and 3 months postpartum and used as three cross-sectional surveys. Interest and use of cessation support and belief and behavior measures were collected at all waves. Key data were adjusted for nonresponse and analyzed descriptively, and multiple regression was used to identify associations. RESULTS: In early and late pregnancy, 44% (95% CI 40% to 48%) and 43% (95% CI 37% to 49%) of smokers, respectively, were interested in cessation support with 33% (95% CI 27% to 39%) interested postpartum. In early pregnancy, 43% of smokers reported discussing cessation with a midwife and, in late pregnancy, 27% did so. Over one-third (38%) did not report discussing quitting with a health professional during pregnancy. Twenty-seven percent of smokers reported using any National Health Service (NHS) cessation support and 12% accessed NHS Stop Smoking Services during pregnancy. Lower quitting confidence (self-efficacy), higher confidence in stopping with support, higher quitting motivation, and higher age were associated with higher interest in support (ps ≤ .001). A recent quit attempt and greater interest in support was associated with speaking to a health professional about quitting and use of NHS cessation support (ps ≤ .001). CONCLUSIONS: When asked in early or late pregnancy, about half of pregnant smokers were interested in cessation support, though most did not engage. Cessation support should be offered throughout pregnancy and after delivery. IMPLICATIONS: There is relatively high interest in cessation support in early and late pregnancy and postpartum among smokers; however, a much smaller proportion of pregnant or postpartum women access any cessation support, highlighting a gap between interest and engagement. Reflecting women's interest, offers of cessation support should be provided throughout pregnancy and after delivery. Increasing motivation to quit and confidence in quitting with assistance may enhance interest in support, and promoting the discussion of stopping smoking between women and health practitioners may contribute to higher support engagement rates.