Objective: To analyze the outcome of graft central thickness after penetrating keratoplasty. Design: Retrospective observational cohort study. Participants: E ight hundred fifty-six consecutive penetrating keratoplasties (772 patients) pe rformed between 1992 and 2001 were analyzed and 772 were included (1 graft per p atient was included). Methods: Slit-lamp examination and ultrasound pachymetry. Main Outcome Measures: Slit-lamp findings, intraocular pressure, and graft cen tral thickness were recorded. Results: Patients were observed for an average of 55 months. The 36-and 60-month graft survival estimates were, respectively, 77 .2%and 71.0%. The average graft central thickness in successful transplants wa s 655 μm at 1 week, 558 μm at 1 month, 533 μm at 6 months, 538 μm at 12 mont hs, 558 μm at 24 months, 561 μm at 36 months, and 568 μm at 5 years. At each postoperative time point, the percentage of eyes with decreased, normal, and inc reased graft central thickness was significantly different according to slit-la mp findings. Of the patients with increased graft thickness, 46.2%had a simple outcome (normal intraocular pressure and normal slit-lamp findings), 28.6%expe rienced rejection, 15.8%experienced a graft nonimmunological event, and 9.4%ex perienced increased intraocular pressure. At each postoperative follow-up, subs equent graft survival was significantly lower in patients with increased graft t hickness as compared with patients with normal or decreased graft thickness. Whe n analyzing only patients with simple outcome, the relative risk of graft failur e was 3.3 if graft thickness was increased at 1 month (P < 0.0001). Conclusions: In conclusion, graft central thickness assessed by ultrasound pachymetry is a u seful method for observing patients who have undergone penetrating keratoplasty. Evenwhen slit-lamp examination reveals no complications, patients with an incr ease in graft thickness above the upper limit of normal for the postoperative ti me point under consideration are at greater risk of failure. Objective: To analyze the outcome of graft central thickness after penetrating keratoplasty. Design: Retrospective observational cohort study. Participants: E ight hundred fifty-six consecutive penetrating keratoplasties (772 patients) pe rformed between 1992 and 2001 were analyzed and 772 were included (1 Grafts per p atient was included). Methods: Slit-lamp examination and ultrasound pachymetry. Main Outcome Measures: Slit-lamp findings, intraocular pressure, and graft cen tral thickness were recorded. Results: Patients were observed for an average of 55 months. The average graft central thickness in successful transplants was 655 μm at 1 week, 558 μm at 1 month, 533 μm at 6 months, respectively. The 36- and 60-month graft survival estimates were, respectively, 77 .2% and 71.0% 538 μm at 12 mont hs, 558 μm at 24 months, 561 μm at 36 months, and 568 μm at 5 years. At each postoperative time point, the percentage of eyes with decreased, normal, and inc reased graft central thickness was signif Of the patients with increased graft thickness, 46.2% had a simple outcome (normal intraocular pressure and normal slit-lamp findings), 28.6% ex pe rienced rejection, 15.8% experienced a graft nonimmunological event, and 9.4% ex perienced increased intraocular pressure. At each postoperative follow-up, subs equent graft survival was significantly lower in patients with increased graft t hickness as compared with patients with normal or decreased graft thickness. Whe n analysis only patients with simple outcome, the relative risk of graft failur e was 3.3 if graft thickness was increased at 1 month (P <0.0001). Conclusions: In conclusion, graft central thickness assessed by ultrasound pachymetry is au seful method for observing patients who have undergone penetrating keratoplasty. Evenwhen slit -lamp examination reveals no complications, patients with an incr ease in graft thickness above the upper limit of normal for the postoperative ti me point under consideration are at greater risk of failure.