Purpose: To study the effectiveness and safety of corneal collagen cross-linking with hypoosmolar riboflavin solution applied to keratoconus patients with thin corneas. Material and Method: In this retrospective study, medical records of keratoconus patients planned for cross-linking surgery and having thinnest corneal thickness (TCT) less than 400 μm after corneal epithelial removal were reviewed. There were 12 patients and 16 eyes in the study cohort. After the epithelium was removed, hypoosmolar solution was applied for 30 minutes and pachymetric measurements were taken. If corneal thickness became more than 400 μm, the cross-linking procedure was started; if not, hypoosmolar solution was continued until corneal thickness reached 400 μm. Maximum keratometry values (K Max), pachymetric measurements, uncorrected distance visual acuities (UDVA), and corrected distance visual acuities (CDVA) were recorded. Comparison between preoperative measurements and measurements taken in sixth postoperative month were performed. Re sults: The mean TCT was 422.75±26.98 μm preoperatively (max: 450, min: 360). The mean TCT was reduced to 373.63±22.41 μm after epithelium was removed (max: 398, min: 325). There was a statistically significant difference between preoperative K max (62.62±5.09) and postoperative K max (61.55±5.80), (p=0.03). On the other hand, the difference between preoperative-postoperative UDVA (p=0.29) and preoperative-postoperative CDVA was not significant (p=058). There were no cases with significant corneal opacity or with any other complication. Dis cus si on: Corneal collagen cross-linking with hypoosmolar riboflavin solution in keratoconus patients with thin corneas is an effective procedure and can be considered as safe regarding preservation of visual acuities and absence of significant corneal opacity.