The purpose of this study was to examine the effect of smoking on the clinical, radiographic outcome of surgical peridontal therapy. The outcome of periodontal surgery was evaluated in 51 systemically healthy subjects that had received maintenance care. The study subject consisted of 26 smokers and 25 non-smokers. The average age of smoking patients was 51 years old and non-smoking patients was 48 years old. Changes of probing pocket depth(PPD) and radiographic bone height, and number of missing teeth compared between smokers and non-smokers during maintenance period after surgical therapy. The clinical parameters were less favorable in the smoking group compared with non-smoking group. The number and percentage of missing teeth were greater in smokers(21.6%) than non-smokers(l2.4%), especially in molars. The mean presurgery PPD was similar in smokers and non-smokers, molars and premolars, but significantly decreased at least 2 years after surgery. The mean PPD reduction was significantly greater in non-smokers than smokers. Both in the smoking and non-smoking group, the mean PPD reduction was significantly greater in premolars than molars. The radiographical evaluation was also less favorable in the smoking group than non-smoking group. The radiographic evaluation of bone height in smokers showed bone loss. On the contrary, bone height of non-smokers showed bone gain during the period of maintenance. But there was no significant difference between molars and premolars. The clinical and radiographic outcomes of the smoking group was less favorable than those of the non-smoking group. Therefore , smoking seems to influence on the clinical and radiographic outcomes of surgical periodontal therapy.