Preterm infants have a high risk of post-discharge feeding problems, but there is a lack of population-based studies in infants born extremely preterm and little is known about underlying mechanisms. The objectives were to assess the incidence of post-discharge feeding problems and underweight in a population-based cohort of infants born extremely preterm in Sweden (EXPRESS) and identify perinatal risk factors. Perinatal health data and prenatal/postnatal growth data was prospectively collected in the cohort. Data on clinical diagnoses related to feeding problems were obtained from the Swedish Patient Register and population prevalence data was also obtained. The main outcome was a composite of post-discharge feeding problem diagnosis and/or underweight at 2.5 years of age. In total, 66 children (19%) had post-discharge feeding problems diagnosed before 2 years and/or underweight at 2.5 years of age. The risk of feeding problems when compared to the general population was significantly higher, with an odds ratio (OR) of 193 (95% confidence interval (CI) 137.6-270.9). The strongest risk factors for feeding problems were the number of days on mechanical ventilation during the first 8 postnatal weeks, OR of 1.59 (CI 95% 1.29-1.98), and the Clinical Risk Index for Babies-score, OR of 1.14 (CI 95% 1.03-1.26). Post-discharge feeding problems and underweight are common in children born extremely preterm. The strongest perinatal risk factor for later feeding problems was early treatment with mechanical ventilation. Identifying infants at risk of post-discharge feeding problems might be useful for targeting of nutritional support.