BACKGROUND Port-wine stains, or capillary malformations, occur in 0.3-0.5% of newborns and have been shown to be very responsive to treatment with a pulsed dye laser (585 nm, 450 microseconds). Lesional characteristics that may help predict the ease of response to therapy have not been delineated. There exists a great range of variation in response to treatment. OBJECTIVE A retrospective study of 133 patients with 140 port-wine stain malformations being treated with the flashlamp-pumped pulsed dye laser was undertaken. Lesion characteristics such as color and location, patient age, and skin type were evaluated as to their correlation with clinical response. Adverse sequelae were evaluated as well. METHODS Charts of treated patients were reviewed and results tabulated. The five treating physicians were each responsible for reviewing and evaluating their own patients. Patients were treated at 8-12-week intervals using slightly overlapping pulses with fluences from 5.5 to 7.5 J/cm.2 RESULTS Factors favoring a positive clinical response were pink lesion color, lesion location of the head and neck, patient age less than 10 years, and patient skin types I-III. Factors having a more negative impact on clinical result include purple lesion color, lesion location on the distal extremities, patient age > 50 years, and skin types IV and V. CONCLUSIONS Examination of various patient and lesional characteristics shows trends that may be useful in a predictive manner regarding ease of treatment with the flashlamp-pumped pulsed dye laser.