Intravascular large B-cell lymphoma (IVL) is a rare subtype of extranodal malignant lymphoma. The proliferation of neoplastic B cells within small blood vessels causes eruptions and other symptoms in a variety of organs. The random skin biopsy is useful for diagnosing this condition in its early stages. In order to assess the diagnostic utility of this method, we examined 3 cases with the aim of comparing the occurrence of tumor cells in lesional and healthy-looking skin by performing a random skin biopsy of 32 separate sites. Our findings from the total of 32 biopsy specimens collected from the 3 cases indicated that 16 of the 17 sites on the lesional skin and 1 of the 15 sites on the healthy-looking skin were positive for neoplastic cells. This finding suggested that IVL cells occurred more frequently in the lesional skin than in the healthy-looking skin.