Objective: To investigate the repeatability of maternal self-reported prenatal, perinatal and early postnatal factors within the IDEFICS (Identification and prevention of dietary-and lifestyle-induced health effects in children and infants) study. Design: Data are from the baseline survey of the longitudinal cohort study IDEFICS in eight European countries. Subjects: A total of 420 parents from eight countries (43-61 per country) were asked to complete the parental questionnaire (PQ) twice at least 1 month apart. Measurements: The PQ assesses prenatal (maternal weight gain), perinatal (child's birth weight and length, Caesarean (C)-section, week of delivery) and early postnatal factors (exclusive breastfeeding, breastfeeding, introduction of solid food). Intra-class correlation coefficients (ICCs) were calculated to compare maternal reports on prenatal, perinatal and early postnatal factors between the first and second PQ. Results: In total, 249 data sets were considered for the analyses. Overall, maternal reports for prenatal and perinatal factors showed higher repeatability (ICC = 0.81-1.00, P