The resemblance between fallopian tube cells and serous borderline ovarian tumors (BOTs) suggests a potential origin link, with salpingitis proposed as a contributing factor in the pathogenesis of BOT. This study aimed to explore the potential association between pelvic inflammatory disease (PID) and the risk of developing BOT. A national population-based case–control study in Sweden included women with BOT between 1999 and 2020 and 10 matched controls. Data from nationwide registers were analyzed using conditional logistic regression, adjusting for age, residential district, educational level and parity. Among 4782 cases and 45,167 controls, 2.0% of cases and 1.3% of controls had a history of PID. Previous PID was associated with an increased risk of BOT overall (aOR, 1.48; 95% CI, 1.19–1.85). Significant association was observed with serous tumors (aOR, 1.76; 95% CI, 1.36–2.29), while not with mucinous tumors (aOR, 0.95; 95% CI, 0.60–1.49). A dose–response relationship between number of PID episodes and serous BOT risk was noted (Ptrend <.001). This study demonstrates that PID is associated with increased risk of serous BOT, with a dose response relationship. The study highlights the potential serious implications of upper reproductive tract infections and inflammation. This underscores the need for further investigation of biological mechanisms and possible impact of PID on serous BOT development.