We studied 40 eyes from patients with pre-existing corneal endothelial cell dystrophy (endothelial cell counts of less than or equal to 1,200/mm2) to assess whether the scleral tunnel incision with internal corneal lip and phacoemulsification in situ procedure affected the cornea. Identification of endothelial cell dystrophy by measuring preoperative endothelial cell counts was important so minor modifications of decreased phacoemulsification power and frequent viscoelastic endothelial coating could be made to prevent damage to the eyes. The procedures had no effect on corneal thickness or endothelial cell counts. Only about one fourth of the eyes studied (11) had more than 10% endothelial cell loss; none of the 11 eyes showed clinical evidence of corneal decompensation. All patients without other underlying pathologies such as macular degeneration attained postoperative visual acuity of at least 20/40. The scleral tunnel incision with internal corneal lip and phacoemulsification in situ procedure, with minor modifications, is safe in patients with endothelial cell dystrophy of the cornea.