Background: Several erbium:YAG lasers are currently available for cutaneous laser resurfacing. Although different laser systems are purported to produce equivalent laser energies to produce similar laser-tissue interactions, no comparative clinical or histologic studies have been performed to objectively demonstrate their relative efficacies. Objective: The purpose of the present study was to examine the in vivo clinical and histopathologic effects of six different erbium:YAG resurfacing lasers. Methods: A blinded, prospective study using six different erbium lasers (Candela, Continuum Biomedical, HGM, MDLT, SEO, Sharplan/ESC) was performed. The facial halves of 12 patients were randomly resurfaced with one of the six laser systems by using an identical laser technique at 5.0 J/cm 2 . Intraoperative skin biopsies were obtained after each of three laser passes in two patients for blinded histologic determination of tissue ablation level and presence of residual thermal damage. Clinical assessments of reepithelialization rates, severity and duration of erythema, side effects, and degree of clinical improvement were made at 0.5, 1, 2, 4, 12, 26, and 52 weeks postoperatively. Results: Irrespective of the erbium laser system used, complete reepithelialization typically occurred at 0.5 weeks and resolution of erythema was noted within 1-2 weeks postoperatively. A mean clinical improvement of 50% was observed, with photodamaged skin showing greater improvement than scarred skin. The most common postoperative side effect was hyperpigmentation, with all affected patients having either darker skin tones or preceding dermal inflammation. Three laser passes were needed to effect total epidermal ablation when using any one of the erbium:YAG systems. Conclusions: Equivalent clinical and histologic results were seen after each of the six erbium:YAG lasers studied. Erbium:YAG laser resurfacing can be used to significantly improve mild cutaneous photodamage and atrophic scars. Lasers Surg. Med. 24:87-92, 1999.