Periodontal diseases are the most common chronic conditions affecting the human race. Recently, increased attention has been given to these diseases because they were found to be related not only to oral health but also to many systemic diseases such as diabetes mellitus or cardiovascular diseases. Nomeclature and classification systems used to describe periodontal diseases have been markedly changed in the last decades what was the source of problems when comparing literary data on prevalence, ethiopathogenesis and treatment in various time periods. The paper presents the contemporary classification of periodontal diseases and the clinical units affecting children and adolescents are given in detail.

        Key words: gingivitis - periodontitis - childhood - adolescence - plaque