For 10 years, a 22-year-old woman had had an erythematous, translucent patch of grouped blisters on her left thigh. A recent increase in the size of the patch prompted the patient to seek treatment. There was no burning or tingling at the site. The patient reported that the erythema occasionally cleared; however, the blisters always remained. She denied fever, weight loss, and other constitutional symptoms. There was no history of radiation therapy, lymphedema, trauma, or surgery at the affected area. She had had mild acne during adolescence; an oral contraceptive was her only medication. A 5-cm patch and an adjacent 1.5-cm patch of grouped, translucent, erythematous, well-circumscribed vesicles with a “frog spawn” appearance were noted on the left lateral thigh (A). A biopsy (B and C) demonstrated dilated lymph vessels lined with a layer of endothelial cells in the papillary dermis; this confirmed the suspected diagnosis of lymphangioma circumscriptum. Drs Jonathan S. Crane and Ronald P. Benjamin and John Schoonmaker, PA-C, of Wilmington, NC, write that lymphangioma circumscriptum is an uncommon condition in which dilated lymph channels form cutaneous vesicular lesions that contain lymphatic and/or hemorrhagic infiltrates. Typically, the cause is idiopathic; however, lesions can appear in patients with postsurgical lymphedema or in those who have undergone radiation therapy. Treatment options include observation, surgical excision to remove communicating tracts, and electrocautery. This patient opted to observe the lesions for further changes. There is no risk of malignant transformation; infection may occur occasionally.