A study of lymphangioma circumscriptum has been carried out over a number of years in an attempt to understand its nature and pathogenesis, with a view to improving treatment. It is postulated that the lesion consists essentially of a collection of large muscular-coated lymphatic cisterns, lying deep in the subcutaneous plane and communicating via dilated dermal lymphatics with the superficial vesicles. It seems that these cisterns do not communicate directly, if at all, with the general lymphatic system but represent a sequestrated part of it. They have been shown by cannulation to pulsate at a slow steady rate producing a rise and fall of pressure within them. It is believed that the vesicles are saccular dilatations of superficial lymphatics, secondary to raised pressure transmitted from the pulsating cisterns beneath. It is suggested that may be possible to treat these lesions more successfully and with better cosmetic results by excising the subcutaneous cisterns and leaving the overlying skin intact.