Objectives: A comparative study is made of two types of flaps in semi-impacted third molar surgery and their relation to the postoperative period (pain, swelling and trismus). Material and methods: Twenty-five healthy patients were subjected to surgical extraction of both semi-impacted lower third molars, located in a similar clinical and radiographic position. In 25 cases the wound was sutured using a reflection flap (healing by first intention), while in the 25 contralateral cases the conventional technique was used (simple approximation of the wound margins). Pain, swelling and trismus were evaluated, during the first week of the postoperative period. Results: There was lesser pain, swelling and trismus after extraction of a semi-impacted third molar when healing took place by second intention (simple approximation of the margins), than in the case of healing by first intention (flap repositioning and margin-to-margin suturing). Conclusions: The postoperative course proved worse when using a reflection flap for healing by first intention than on suturing by simple approximation of the wound margins.