Objectives: To examine the prospective association between menstrual symptoms before pregnancy and preterm birth. Methods: Secondary analysis of data from 14 247 young Australian women born between 1973 and 1978 who participated in a longitudinal, population-based cohort study between 1996 and 2015. Women were first surveyed at 18-23 years, and seven waves of data were collected at roughly three-yearly intervals. At each survey, women were asked about “severe period pain,” “heavy periods,” and “irregular periods” within the last 12 months. From 2009 onward, information on their children was collected, including birth dates and preterm birth (<37 >weeks). Logistic regression using generalized estimating equations was used to examine prospective associations between self-reported menstrual symptoms before pregnancy and risk of preterm birth. Results: Data from 6615 mothers who had 12 337 live singleton births were available for analysis. Among all births, women reporting severe period pain (adjusted odds ratio [aOR] 1.34 [95% CI 1.10-1.62]) or heavy periods (1.25 [1.02-1.53]) before pregnancy had higher odds of preterm birth. However, in analyses stratified by birth order, only severe period pain (2.05 [1.41-2.99]), heavy periods (1.77 [1.23-2.55]), or irregular periods (1.58 [1.10-2.28]) before a second or subsequent birth were associated with an increased risk of preterm birth. Conclusions: Severe period pain, heavy periods, and irregular periods before a second or subsequent birth may be associated with preterm birth.