AIM: Case reports (CRs) are often the first publication of a new treatment, but randomized clinical trials (RCTs) are needed to confirm the data. The aim of this study was to evaluate how many therapies published as CRs were followed by RCTs of these therapies over a 20-year period. MATERIAL AND METHODS: Two researchers conducted a search through international periodontal journals and found the CRs on periodontal treatments published from 1984 to 1986. Subsequent electronic searches made it possible to verify how many of the treatments published as CRs were also investigated through RCTs over the following 20 years. RESULTS: Thirty-one different therapies were selected out of the 33 published CRs; 15 (48%) of these 31 treatments were investigated by RCTs over the next 20 years. CONCLUSIONS: As 52% of the CRs were not validated by RCTs, practitioners should view their results with caution.