Seventeen cases of intravascular fasciitis were reported from the files of the AFIP (14 cases) and the Pathology Department, Thomas Jefferson University Hospital (three cases). It is characterized by the histologic features of nodular fasciitis but with intraluminal, intramural, and extramural involvement of small to medium-sized veins and arteries and multinodular or serpentine growth along the course of affected blood vessels. A painless, slowly growing mass was most common. Fourteen patients (82%) were under age 30 (range 1/2-57 years); the sex ratio was about equal. Seven cases were located in the upper extremity (three hand, two wrist or forearm, two shoulder), three on the ankle or lower leg, five on the head and neck, and two in the chest wall and breast. Most cases were small with a mean diameter of 1.5 cm, but two were elongated masses measuring 4-5 cm in length. At surgery, four cases showed intimate association with large veins or arteries. This type of fasciitis is rare and has been found in only one of 14 consecutive cases of modular fasciitis operated at this university hospital between 1969 and 1978. Six of 15 consultation cases were originally confused with sarcoma. Intravascular fasciitis is benign. Seven patients were free of disease from 2.5 to 20 years (mean 9.5 years); two patients had local recurrences.