Among the complications of the frontal sinusitis, osteomyelitis of the frontal bone may cause subperiosteal, epidural and cerebral abscess, subdural empyema, cavernous sinus thrombosis and meningitis. Subperiosteal(pericranial) abscess which is called Pott's puppy tumour is one of the characteristic sign resulting from osteomyelitis of the frontal bone. Recently, we have experienced a case of Pott's puffy tumour with epidural abscess caused by acute frontal sinusitis. Acess to the sinus wall was done through the coronal incision and flap elevation. Anterior wall of the frontal sinus and surrounding calvaria showed osteomyelitic change and posterior wall was destructed. At the first operation, we removed pericranial abscess, all of the osteomyelitic bone, edematous sinus mucosa and epidural abscess through craniotomy approach. After antibiotic therapy and irrigation with antibiotic solution for six weeks, the remained granulation tissue and the remnant osteomyelitic sinus wall were removed clearly and meticulously at the second operation. We obliterated the bony defect by the Original Bone Cement.