A total of 202 patients with port wine stains have been studied and many aspects of their clinical condition detailed. Employing ther argon laser, 136 test spots have been carried out in 132 patients and the results have been analyzed and correlated with clinical aspects of the lesions. Altogether, 85 treatments were performed in 54 patients and the results were examined in the same way as the test spots. Good to excellent results were obtained in 75 percent of test spots and 60 percent of treatments in that significant lightening of treated areas was achieved. While elimination of lesions was rare, considerable amelioration was common. Scarring was uncommon but was the most appreciable complication. Residual lesion was the most common cause of fair or poor results. The value of secondary treatment is suggested but remains to be established. The directions of ongoing clinical study are outlined.