Eighty patients (99 eyes) with primary pterygia were treated with excision, with or without additional therapy, and were followed up for three to eight years after treatment. Of 29 eyes that underwent excision and postoperative instillation of 0.02% mitomycin C, there were only two recurrences. The other eyes were treated with excision only, excision and radiation, or excision and 0.04% mitomycin C. Instillation of 0.02% mitomycin C reduced the recurrence rate significantly (P less than .01). Only one of the 29 eyes (3%) treated with excision and 0.02% mitomycin C had a complication, the lowest rate of all groups postoperatively. We found the postoperative instillation of 0.02% mitomycin C, twice a day for five days, to be effective and safe in the treatment of primary pterygium.