A 58-year-old woman had successful phacoemulsification with intraocular lens (IOL) implantation in January 2001. Two years later, nonpenetrating glaucoma surgery with mitomycin-C (MMC) 0.02% was performed for uncontrolled glaucoma. Two months later, opacification of the anterior IOL surface was observed. The IOL was removed and a hydrophobic acrylic AcrySof IOL (Alcon) implanted. The opacified IOL was studied by flame atomic absorption spectrometry, which showed the presence of calcium carbonate. A new IOL of the same model was placed in an aqueous solution with calcium carbonate and basic pH, and the same opacification developed. We hypothesize that the change in aqueous humor pH after glaucoma surgery and the characteristics of the IOL precipitated deposition of calcium.