Objective The aim of the study was to observe and compare the effects of dexamethasone on pain, swelling and trismus administered as one dose preoperatively sub mucosal (study group 2) versus intramuscular injection (study group 1) keeping control as those who received no dose of steroid in the management of third molar surgery. Materials and methods The group 2 (20 patients) is the study group in which all the patients had single dose of preoperative sub mucosal dexamethasone of 4 mg/2 ml. The group 1 patients (20 patients) received single dose of preoperative intra muscular dexamethasone of 4 mg/2 ml. The control group (20 patients) did not receive steroid in any form. The post operative pain, swelling and trismus were assessed for all the groups. Results The submucosal dexamethasone group showed marked improvement in the mouth opening in the follow ups than the intra muscular dexamethasone group. In those five cases of bilateral impaction, in study groups 1 and 2, the mouth opening was very much significant when sub mucosal dexamethasone was given. Conclusion The pre operative use of submucosal dexamethasone effectively reduces the post operative pain, swelling and trismus showing statistically significant results. The number of post operative use of analgesic tablets taken by the patients in the study group 2 were less compared to the study group 1 and the control group showing clinically significant results.