A high-power argon laser system (maximum 20 W on the skin) was used with a 2-mm-spot size for the treatment of port-wine stains (PWS). Five hundred and thirty test treatments were evaluated. With short pulse times (< 15ms), relatively specific damage to vessels could be demonstrated histologically, but sufficient clinical lightening of PWS was seen only in 30% of patients due to the resulting low energy fluence (∼=10 Jcm−2_. With higher energy fluences and longer pulse times, clinical lightening increased but vessel specificity was lost. Overall results showed that with a high-power argon laser comparable clinical blanching can be achieved as with conventional argon lasers, but the necessary energy fluences are lower (∼=15 Jcm−2) leading to less pain under treatment and a minimal incidence of side-effects.