Purpose: To compare long-term biocompatibility of single-piece poly(methyl methacrylate) (PMMA) and poly(hydroxyethyl methacrylate) (P-HEMA) intraocular lenses (IOLs). Setting: District General Hospital, United Kingdom. Methods: In a prospective trial of 250 eyes that had uncomplicated extracapsular cataract extraction, 2 groups of 125 eyes each were matched for age and sex. One group received single-piece looped PMMA IOLs and the other, single-piece solid-haptic P-HEMA IOLs. In all eyes, the IOLs were implanted in the capsular bag at the time of surgery using the envelope technique. Results: Twelve years after surgery, 75 eyes were available for examination. In the PMMA i group (40 eyes), 50% had a visual acuity of 20/20 and 50% had intact capsules, many of them with a degree of fibrosis. In the P-H EMA group (35 eyes), 71 % had an acuity of 20/20 and 80% had intact capsules (P = .0085). Conclusion: In the long term, biocompatibility was better in the P-HEMA group than in the PMMA group. (C) 1999 ASCRS and ESCRS.