Objective To analyze the distribution of types and characteristics of periodontal diseases in 34 677 patients visiting the Department of Periodontology, Peking University School and Hospital of Stomatology.Methods Clinical data of 34 677 patients who had the electronic periodontal examination charts from 2007 to 2012 were collected and analyzed.Results Out of 34 677 patients, 32 517 (93.77％) were diagnosed as chronic periodontitis(CP), 1 642(4.74％) were aggressive periodontitis(AgP) and the rest 518(1.49％) patients were classified into some other types of periodontitis.There were more female patients than male ones.Most of patients were between 25 to 54 years olds.Only 7 306(21.07％) patients had more than two periodontal examination charts which represented regular re-visits to the doctors.The majority of patients had severe periodontitis.Conclusions Most of the patients visiting the Department of Periodontology were older aged and diagnosed chronic periodontitis.They had more severe periodontitis conditions but less re-visits.Therefore it is very important for dentists to enhance the oral health education and make early diagnosis and treatment of periodontal diseases for patients.Dentists also should do more follow-up and maintenance works for patients after the initial treatments.