Recently, osteomyelitis which develops subacutely or chronically from the start, and subacute or chronic osteomyelitis which follows an acute attack treated with antibiotics, have been increasing, although typical acute or chronic osteomyelitis have decreased.We would like to present a case with severe reumatic arthrosis which had Brodie's abscess and subacute osteomyelitis on bilateral mandible and was treated successfully with antibiotics and some surgical procedures like trepanation.The patient, a 75-year-old man, visited our clinic January 18 th of 1983 complaining of pus discharge from right side of the mandible. He had been suffering from severe rheumatic arthrosis and had been treated with steroids for the past several years. Six months before his first visit to us, he got acute osteomyelitis on the right side of the mandible after extraction of the right lower first molar. He was admitted to another clinic and was treated for 3 months, but did not recover from the osteomyelitis.At the first visit to us the clinical examination revealed low grade fever, pus discharge from fistulae on the right lower molar gum and the anterior area of the right ear, and a cystic lesion similar to Brodie's abscess at the right side of the mandible were observed on X-rays.He was admitted and treated with antibiotics and trepanation. After treatment the pus discharge stopped.Two years later, simular subacute localized osteomyelitis occurred on the left side and frontal portion of the mandible and was treated in the same way.About 2 years after the second treatment, he died of renal disease without the recurrence of osteomyelitis on either mandible side.