The present study was conducted to clarify the effects of chewing a quid containing areca nut and tobacco on periodontal tissue and oral hygiene status. A total of 365 subjects (168 chewers and 197 non-chewers with a mean age of 32.5 ± 0.7 and 30.4 ± 0.8 years, respectively) were enrolled. Clinical data on periodontal tissues, oral hygiene status, as well as information on bleeding from gums, ulcers in the oral cavity, or a burning sensation in the soft tissues, were collected as indicators of the possible presence and extent of periodontal lesions. The results indicated that a significantly higher number of quid-chewers suffered bleeding from the gums, halitosis, difficulty in opening the mouth and swallowing solid food, a burning sensation in the soft tissues, and ulcers in the oral cavity than non-chewers. There was no significant difference between quid-chewers and non-chewers with respect to oral hygiene measures adopted. However, clinical examination using the oral hygiene index score indicated that the oral hygiene status of quid-chewers was significantly deteriorated. The effect of quid-chewing on the periodontium, i.e. the occurrence of periodontal pockets, gingival lesions and gum recession, were significantly higher in quid-chewers than in non-chewers. Age, sex and smoking adjusted odds ratios for quid-chewers against non-chewers using logistic regression analysis indicated that, in general, chewers were at significantly higher risk for various oral complaints and periodontium status. The present data indicate that chewing quid comprising areca nut and tobacco has adverse effects on periodontal tissues, oral hygiene and incidence of oral lesions. (J. Oral Sci. 50, 57-62, 2008)