Three patients with polyarteritis nodosa associated with periosteal new bone formation in the lower extremities are described. Seven cases with many similar features have been collected from the literature. Pain, swelling, and skin changes in the lower extremity with periosteal reaction seem to characterize one of the syndromes found in polyarteritis nodosa.Diffuse periosteal new bone formation is an uncommon feature of polyarteritis nodosa, but it does occur in association with a specific set of symptoms and findings.The unusual roentgenographic findings in case 1 prompted us to review the roentgenograms of other patients with polyarteritis nodosa. From 1968 to 1972, one hundred fifty-eight patients with a diagnosis of polyarteritis nodosa have been seen at the Mayo Clinic. This diagnosis was proposed on the basis of clinical findings and confirmed by histologic examination of biopsy specimens. Approximately half of these patients had had roentgenograms made of one or more of their extremities. A review of these roentgenograms disclosed two additional cases associated with periosteal new bone formation. REPORT OF CASESCase 1. A 46-year-old male teacher came to the Mayo Clinic in November 1971 because of pain and ulceration of the skin on the dorsum of the right foot. He had had recurrent ulcers on the right, and occasionally the left, ankle and foot since 1963, with exacerbations usually in the fall of each year. Investigation at another institution in March 1967 revealed electromyographic evidence of a peripheral neuropathy involving both lower extremities. Skin biopsy a t that time was reported to be negative. In December 1970 he was again extensively investigated at the same institution. T h e skin biopsy at that time revealed acute and subacute inflammation in the superficial dermis. T h e eosinophil count and the serum glutamic-oxalacetic transaminase (SGOT) value were increased.When the patient was first examined at the Mayo Clinic he complained of aching pain of such severity that he was unable to perform his teaching duties. There was mild swelling of the lower part of the right leg and the ankle, with a blotchy bluish discoloration of the skin. There were numerous circular brown macules and a large ulcer. L'aricose veins were not prominent and arterial pulsations were normal.Relevant laboratory data were: hemoglobin, 10.4 g/ 100 ml; erythrocyte count, 4,43O,OOO/cu mm; leukocyte count, 8,20O/cu mm with 11.5% eosinophils; peripheral blood smear, consistent with blood-loss anemia; erythrocyte sedimentation rate, 73 mm in 1 hour (Westergren); SGOT, 15 IU/liter; sulfobromophthalein (BSP) retention, 23% in 1 hour; serum protein electrophoresis, albumin 3.43 g/ 100m1, al-globulin 0.22 g/100 ml, =,-globulin 0.73