A study of 27 cases of pseudoxanthoma elasticum (PXE) has been made from the point of view of internal medicine. This disease is hereditary and is characterized by typical manifestations of the eyes, skin, mucous membranes and cardiovascular system. Twelve patients died at the time of the investigation, two of malignant diseases, one of gastrointestinal bleeding, and nine of cardiocerebrovascular diseases. All the 15 living patients had typical skin lesions which caused only cosmetic discomfort. In most cases these skin lesions were the first symptom of the disease. Angioid streaks were found in all the patients, nearly all of whom had impairment of vision which had mostly occurred about 20 years later than the skin lesions. The patients with impaired vision also showed different degrees of macular and peripapillary atrophy and retinal‐pigment proliferation. Manifestations of cardiocerebrovascular disease appeared in many of the patients; these symptoms were recognized somewhat later than the eye lesions, but in some cases they had occurred at an early age. Gastrointestinal bleedings occurred in four patients, in one of whom they proved fatal. No characteristic abnormalities were found in the extensive laboratory survey.