PURPOSE: To evaluate the effect of benzalkonium chloride-assisted (BAC) transepithelial collagen crosslinking (CXL) in eyes with progressive keratoconus and a minimum follow-up of 6 months. SETTING: Department of Ophthalmology, Antwerp University Hospital, Antwerp, Belgium. DESIGN: Cohort study. METHODS: Eyes with progressive keratoconus had CXL treatment without epithelial debridement. The standard CXL irradiation was preceded by instillation of proparacaine drops 0.5% preserved with BAC 0.005% every 5 minutes for 30 minutes. Selected parameters of refraction assessed by Placido disk (Eyesys) and Scheimpflug (Pentacam) examinations were compared before CXL and after CXL at 6, 12, and 18 months. RESULTS: The study enrolled 53 eyes of 38 patients. Sphere, cylinder, as well as maximum keratometry (K max) simulated K values (steep, flat, astigmatism), and refractive power values (steep, flat, astigmatism) measured using the Placido disk device remained stable over the 18-month follow-up. Only corrected distance visual acuity showed a statistically significant improvement at 6 months and 12 months. The Scheimpflug device measurements of maximum K and pachymetry at the thinnest point showed statistically significant progression throughout the study. No patient developed corneal haze or other complications. CONCLUSION: Transepithelial CXL using proparacaine drops 0.5% preserved with BAC 0.005% was less effective than standard CXL in stabilizing progressive keratoconus.