This report describes periodontal findings from a comprehensive study of smokeless tobacco use in professional baseball players. Subjects consisted of 1,094 players, coaches, and training staff of seven major league and their associated minor league teams. Before being examined, subjects completed questionnaires on patterns of smokeless tobacco use (validated by blood chemistry studies), rinsed their mouths under supervision, and were cautioned not to discuss their use of tobacco with the dental examiners. They then received a complete oral examination that included recording of all mucosal abnormalities, missing teeth, caries, extrinsic stain, attrition, Plaque Index, Gingival Index, pocket depth, attachment loss, and gingival recession. More than 50% of team members reported using smokeless tobacco, and 39% reported use during the current week. Among current week users, 46% had oral mucosal lesions, located primarily in the mandible at sites where the smokeless tobacco quid was placed. The use of smokeless tobacco was not necessarily associated with severe forms of periodontal disease, and the presence of poor oral hygiene and gingivitis in these users was not related to the development of oral lesions. However, sites adjacent to mucosal lesions in smokeless tobacco users showed significantly greater recession and attachment loss than in sites not adjacent to lesions in users or comparable sites in non-users.