AIM: To investigate the long term ( >= 5y) efficacy, predictability, and safety of laser in situ keratomileusis (LASIK) in eyes with thin corneas [central corneal thickness (CCT) <500 mu m]. METHODS: A total of 339 patients met the criteria of this study. Finally, 175 eyes of 89 patients who had thin corneas and underwent LASIK >= 5y ago returned to our clinic and included in this study. Preoperative parameters recorded included uncorrected visual acuity (UCVA), corrected distance visual acuity (CDVA), manifest refraction, CCT and corneal topography. At returning visits, in addition to visual acuity and manifest refraction, ultrasound CCT and corneal topography were performed. Optical coherence tomography was used to measure the CCT, LASIK flap thickness, and residual stromal bed thickness (RSBT). Safety index, efficacy index, percentage of eyes within +/- 0.5 D and +/- 1.0 D of refraction, percent tissue altered (PTA), and percentage stromal bed thickness (PSBT) were calculated. RESULTS: The safety index was 1.09 and efficacy index was 0.99. The percentages of eyes within +/- 0.5 D and +/- 1.0 D were 71.2% and 87.7%, respectively. The mean PTA was 40%+/- 6% (range 20% to 55%); 76 eyes (43.4%) had PTA <40% and 99 eyes (56.6%) had PTA >= 40%. The mean RSBT was 303 +/- 27 mu m (range 240 to 390 mu m), and 2 eyes had RSBT<250 mu m. The mean PSBT was 61%+/- 9% (range 51% to 85%). No eyes developed ectasia. CONCLUSION: In this cohort with the PSBT of 50% or more, LASIK is safe with follow-up for at least 5y.