We assessed changes in periodontal treatment needs among patients with diabetes and the risk factors involved in this phenomenon. The sample consisted of 120 dentate subjects, all of whom were regular patients at the Salo Regional Hospital Diabetes Clinic. They underwent periodontal examination in 1999 and were re-examined in 2001. The drop-out rate was 4%. Clinical periodontal examination included identification of visible plaque, the presence of calculus, and use of the Community Periodontal Index of Treatment Needs (CPITN) index. Diabetes-related factors consisted of information about duration of diabetes, complications, and HbA1c values. Oral health-related factors were collected by questionnaire. The CPITN index proved to be insensitive to change. Pathological pockets (CPITN 3 or 4) were found in 80% of subjects (n = 115) and 48% of sextants (n = 627); in 1999, the corresponding rates were 77% and 49%. The tooth-based individual CPITN index (code 3 or 4) revealed periodontal deterioration in 38 patients. Smoking and infrequent interdental cleaning were significant factors explaining periodontal deterioration in logistic regression. Risk factors should be taken into account when planning prevention, treatment, and supportive periodontal therapy strategies. In diabetes care, the common risk factor approach can be implemented to promote oral health among individuals with diabetes.