Purpose. To assess the risk and incidence of rejection in patients who underwent bilateral penetrating keratoplasty (PK) and had at least one rejection episode. Methods. The records of patients undergoing PK between January 1994 and December 2003 were retrospectively reviewed. Inclusion criteria were bilateral PKs and at least one rejection within 18 months of either PK. Exclusion criteria were PK performed elsewhere, multiple grafts in the same eye, and fewer than 18 months between PKs in the two eyes. Results. Eighty-three patients had bilateral PKs (56 women and 27 men) at least 18 months apart and had a rejection episode within 18 months of at least one surgery. Their mean age was 57.1 +/- 17.7 years. The mean follow-up after the first and second PKs were 9.6 +/- 5.4 and 4.1 +/- 3.7 years, respectively. Kaplan-Meier Survival analysis showed that PK in the second eye did not impose an increased risk of rejection in the first eye. There was no significant difference in the frequency of rejections between the two eyes during the first 18 months after the second PK. The first eye was significantly more likely to have a rejection during the first 18 months after the first PK than during the first 18 months after the second PK (P=0.01). Conclusions. Having a PK in the second eye does not impose a significantly increased risk of rejection for the first eye when PKs are performed at least 18 months apart. There is an indefinite risk for rejection. Lifelong regular follow-up and immediate evaluation for new symptoms are essential
