AIM: The aims of this study were to identify the most cited articles in Periodontology published from January 1990 to March 2005; and to analyse the differences between citation Classics and less cited articles. MATERIAL AND METHODS: The search was carried out in four international periodontal journals: Journal of Periodontology, Journal of Clinical Periodontology, International Journal of Periodontics and Restorative Dentistry and Journal of Periodontal Research. The Classics, that are articles cited at least 100 times, were identified using the Science Citation Index database. From every issue of the journals that contained a Classic, another article was randomly selected and used as a Control. RESULTS: Fifty-five Classics and 55 Controls were identified. Classic articles were longer, used more images, had more authors, and contained more self-references than Controls. Moreover Classics had on the average a bigger sample size, often dealt with etiopathogenesis and prognosis, but were rarely controlled or randomized studies. CONCLUSIONS: Classic articles play an instructive role, but are often non-Controlled studies.