Introduction. To determine the effect of corneal collagen cross-linking treatment on keratoconus and post-LASIK ectasia particularly after an abbreviated exposure to ultraviolet light exposure. Materials and methods. Fifty-one eyes of 34 patients were treated with epithelium-off UVA-ribofl avin corneal collagen cross-linking for either 20 minutes or 30 minutes as part of a US.FDA clinical study. The study involved eyes with keratoconus but with no prior operation (virginal), patients who had undergone prior intracorneal ring segments, those with keratoconus regression after keratoplasty, and those with post-LASIK ectasia. We report follow up results from three months to one year. Results. In the virginal keratoconus group all 83% of eyes having 20-minute UVA exposure and 75% of those having 30-minute of UVA exposure experienced corneal fl attening or stabilization at 6 months post-operatively with visual improvement in both groups. The average patient age in the virginal keratoconus group was 34.5 years. Seventy fi ve percent of virginal keratoconus eyes of patients under age 40 but only 33% of eyes of patients over age 40 experienced statistically signifi cant corneal fl attening at six months postoperatively. Average vision improved at six months post-operatively over pre-operative levels by-0.0744 logMAR units in the 20 minute group, and by-0.0869 logMAR units in the 30 minute group. Post-LASIK ectasia patients, with an average age of 58.2 years, had slight overall curvature fl attening of-0.75D but without visual improvement one year post-operatively. No one experienced peri-operative complications. Topographic subtraction mapping revealed variations in the power of the cross-linking effect on different portions of the cornea Conclusion. Cross-linking appears safe. It is effective in most young patients causing corneal fl attening and can stabilize eyes with post LASIK ectasia but acts more slowly in older patients. The cross-linking effect may be more pronounced in individuals with darker pigmentation. Cross-linking can produce occasional very signifi cant corneal fl attening. The cross-linking effect increases with time.