Objective: Quantitative studies examining the occurrence of childbirth-related posttraumatic stress disorder (CB-PTSD) following severe perineal rupture are lacking. The objective of this population-based study was to investigate the prospective associations between the degree of perineal tear during childbirth and CB-PTSD symptoms, when adjusting for known covariates (maternal age, years of school education, premature birth, and parity). We hypothesized that women with different degrees of perineal tear will differ regarding (1) the level of CB-PTSD symptoms at 8 weeks and 2 years postpartum and (2) the rate of change in CB-PTSD symptoms from 8 weeks to 2 years postpartum. Method: Secondary data analysis from the Akershus Birth Cohort, a large population-based prospective cohort study using self-report questionnaires and hospital record data. Results: The degree of perineal tear was significantly associated with CB-PTSD symptoms at 8 weeks and 2 years postpartum. However, the degree of perineal tear was not significantly associated with the change in CB-PTSD symptoms over time. Similar patterns were found for both total CB-PTSD symptoms as well as for avoidance and intrusion symptoms only. Conclusion: Results seem to support a dose–response model, suggesting that the higher the severity of the perineal tear, the higher the posttraumatic morbidity.