A 39-year-old man underwent phototherapeutic keratectomy via excimer laser for recurrent corneal erosions secondary to basement membrane dystrophy with the subsequent development of irregular astigmatism and central stromal opacity. The cornea was scraped and treated with 0.02% mitomycin C using a total of 14 drops over a period of 6 days. Corneal edema developed as a consequence of low endothelial cell count with dysfunctional cells. A corneal transplant restored acuity of 20/20 with binocular vision. It is believed that the underlying endothelium was exposed to toxic doses of mitomycin C sufficient to damage and destroy vital cells. The author reports this case not to criticize the use of mitomycin C in visually disabling post-phototherapeutic keratectomy or photorefractive keratectomy haze but to apprize colleagues of a potential pitfall. The author believes that the use of mitomycin C as a 1-time application at the end of surgery is a safe and valuable adjunct to recover vision when no other is known. However, continued topical application of mitomycin C to the central cornea, in the face of an epithelial defect or an epithelium with inadequate barrier function, increases the risk of endothelial damage.