This study examined periodontists' ability to self-assess their knowledge of periodontics. Self-assessment was measured as the difference between actual knowledge and perceived knowledge of two topics of clinical practice of periodontics: periodontal disease therapy and dental implant therapy. Other variables included were learning needs, motivation to learn, and background characteristics (number of years since graduation from a periodontics training program, classification as Diplomate or non- Diplomate, number of years since achieving Diplomate status, classification as private practitioner, academician, or private practitioner with a part-time academic position, and number of credit hours spent in continuing education per year). A questionnaire was e-mailed to 1,800 periodontists practicing in the USA. Two hundred and nineteen subjects participated in the periodontal disease therapy questionnaire and 200 in the dental implant therapy questionnaire. The results showed a significant difference between actual and perceived knowledge for both topics. Correlation coefficients showed no correlation between participants' actual knowledge and perceived knowledge of periodontal disease therapy and a low to moderate correlation between actual and perceived knowledge of dental implant therapy. Also, the results showed that need and motivation are not related to self-assessment ability, but actual knowledge may be related to moderate-high need and motivation; and, that among the background characteristics, Diplomate status is related to a better ability to self-assess, and fewer years since achieving Diplomate status is related to higher actual knowledge and perceived knowledge. In conclusion, periodontists' ability to selfassess their knowledge of periodontics is at best moderate. The concern that practitioners believe that they have higher knowledge in areas in which objectively measured knowledge is significantly lower continues to be valid.