Purpose: The aim of this study is to evaluate the association between body mass index (BMI) and endometriosis in Korean women. Materials and Methods: In a hospital-based case-control study, 134 endometriosis cases and 282 ovarian teratoma cases as controls were selected. All cases were histologically confirmed after laparotomy or laparoscopic surgery, and they were categorized by BMI, as < 18.5, 18.5-22.9, 23-24.9, and > 25 kg/m², respectively, according to the World Health Organization (WHO) guidelines for Asia-Pacific populations. Diagnosis for recurrences evaluated mainly by ultrasound or surgery. The authors collected requisite patient information from medical records of seven years. Results: Development of endometriosis was not significantly related to varying BMI. However, when comparing overall median BMI values in endometriosis [21.43 (19.59, 23.61)] and teratoma [22.19 (20.41, 24.61)], BMI was significantly lower in endometriosis cases than in teratoma cases (p = 0.014). There was no significant relation between the BMI groups and American Fertility Society (AFS) stages (Spearman’s r = 0.06584, p = 0.4498). In both of endometriosis and ovarian teratoma patients, the patients with higher BMI than 23 kg/m² showed elevated recurrence rates (p = 0.024, HR = 2.104 and p = 0.026, HR = 4.417, respectively). Yet, considering varying BMI groups and recurrence rates, recurrence rate had no association among 46 recurrent endometriosis and teratoma cases (p = 0.338). Conclusion: In this study, lower BMI was observed to be possibly associated with endometriosis in comparison to that of other benign disease. BMI did not affect disease severity, whereas obesity was related to the recurrence of endometriosis.