Background: This study compared postoperative symptoms in patients treated preoperatively with a single dose of £20 mg oral steroid during third molar surgery. Methods: A total of 450 patients were categorized randomly into three groups containing 150 patients each. Patients were in their second or third decade and had no specific medical history and findings involving infections of the mandibular third molar area. Two groups received preoperative steroids orally one hour before the operation; one group received 10 mg prednisolone and the other received 20 mg. No steroids were administered to the control group. Patients were asked to report by questionnaire any changes in postoperative symptoms, such as pain, facial oedema, or gastrointestinal disorders, and in masticatory disorders, trismus, or swallowing discomfort. They reported daily from days 1 to 6 post-extraction by evaluating their experience over the preceding 24 hours. Results: A single preoperative oral administration of £20 mg prednisolone had no significant effect on postoperative symptoms of pain, facial oedema, or gastrointestinal upset, or on masticatory symptoms, trismus, or swallowing discomfort in mandibular third molar surgery. Conclusions: A single oral dose of £20 mg prednisolone before third molar extraction may not be helpful for the relief of postoperative symptoms.