Among various methods of management for malignant tumors of larynx and pharynx, good therapeutic results can not be obtained without surgical treatment. But old age with geriatric problem, poor general condition and preoperative radiotherapy still causes many postoperative complications, especially pharyngocutaneous fistula that is very troublesome and sometimes threatens life. The author analyzed and evaluated the effect of metronidazole in the prevention of infection from anaerobic bacteria that is present as a normal flora on the upper aerodigestive tract and if infected eventually causes the pharyngocutaneous fistula. A retrospective investigation of 76 cases medicated penicillin plus gentamicin without metronidazole and a prospective investigation of 20 cases medicated above antibiotics with metronidazole who underwent total laryngectomy, partial laryngectomy and Commando operation with or without radical neck dissection was performed. The results obtained are as follows : 1) The number of complications due to infection in without metronidazole medication group were 12 cases of wound infection(15.8%), 10 cases of pharyngocutaneous fistula(13.2%), 4 cases of skin necrosis(5.2%) and a case of pneumonia(1.3%). 2) There were no postoperative wound infection, pharyngocutaneous fistula skin necrosis except a case of pneumonia(5.0%) due to aspiration in metronidazole medication group. 3) Among causative organisms isolated from the patients with wound infection and pharyngocutaneous fistula(total 15 cases, 7 cases were overlapped), the incidence of aerobic and anaerobic bacteria were 66.6%, 26.7% respectively. But in consideration of difficulty of anaerobic culture, more higher percentage of anaerobic bacteria was expected. On the basis of the above results, it is recommendable to use the metronidazole combination with penicillin and getamicin in the prevention of pharyngocutaneous fistula following surgery for malignant tumor of larynx and pharynx.