Portwine stain disfigurement is caused by several factors. To what extent and in which proportion these factors influence the overall perceived disfigurement is incompletely understood. In this study, the contribution of seven portwine stain characteristics to overall portwine stain disfigurement was assessed. Color slides were taken from 90 patients with untreated portwine stains in the head/neck area. From these slides, overall portwine stain disfigurement was judged by a panel of 16 lay persons. The reliability of the average ratings of this panel was established with weighted kappa analysis (kappa = 0.51) and by calculating the Cronbach alpha coefficient (0.99). Using a previously tested multi-item questionnaire, the following portwine stain characteristics were rated quantitatively by a panel of five professionals: color, patchiness, boundary, size, shape, surface structure, and hypertrophy of the underlying tissue. By means of multiple linear regression analysis, the ratings for overall portwine stain disfigurement (panel of lay persons) were compared with the ratings for the individual portwine stain characteristics (panel of professionals). From the results of this analysis, the percentual contribution of each of the characteristics to overall portwine stain disfigurement was calculated. Size turned out to be the most important portwine stain characteristic, being responsible for almost half of the overall disfigurement. Color and boundary are the next two most important characteristics, contributing 18.7 and 12.4 percent, respectively. The other four characteristics together account for 10 percent. In our model, 13 percent of overall portwine stain disfigurement remains unexplained. We expect patient features to account for this. We feel that these results may have consequences for laser treatment of portwine stains. Reducing the size and fading out the boundary of the stain probably reduce overall portwine stain disfigurement more effectively than primarily trying to lighten the often persistent center of the stain.