Objective: Swelling, pain and trismus after surgical removal of the mandibular third molars are most common and expected postoperative complication. The aim of this study was to assess the association of those postoperative complications and BMI after surgical removal of the mandibular third molars. To the best of our knowledge, this is the first clinical trial which studies this connection in patients who had identical tooth position, degree of bone impaction and Parant class in surgical removal of the lower third molars. Material and methods: 84 patients who required surgical removal of their lower third molar were enrolled in this study and were divided into 4 groups dependent on their BMI. All the surgical procedures were performed by the same oral surgeon and assistant, using the same surgical approach. Correlation between body mass index and the occurrence of swelling, pain and trismus after surgical removal of the lower third molar were observed in the first three postoperative days. Results: Data was tested by one-way analysis of variance (Welch's ANOVA).The assessment of data normality was conducted by the Kolmogorov-Smirnov test. The differences were tested intragroup with the Games-Howell test. The level of significance was set at 0.05. In contrast to the effect of BMI on pain where a statistically significant difference was demonstrated within the first 24 postoperative hours: 4 hours (p = 0.014), 6 hours (p = 0.034, p = 0.049), 12 hours (p = 0.00, p = 0.023 ) and 24 hours (p = 0.010), no statistically significant correlation was found for swelling and trismus in the exception on first postoperative day between underweight and normal weight groups (p = 0.026), and underweight and overweight groups (p = 0.014). Conclusion: The study showed that body weight above normal had an effect on pain levels within the first 24 hours of the procedure. Also, on the first postoperative day, difficulty opening the mouth is visible in underweight patients compared with the normal and overweight patients.