As periodontal disease and diabetes mellitus (DM) have bidirectional interactions, an effective approach to periodontal treatment for patients with diabetes in the clinical setting is essential. This paper reports an effort in collaborative care for patients with periodontitis and diabetes between dental and medical professionals, and provides a preliminary evaluation regarding the clinical outcomes. We have introduced a clinical pathway program at our institution applicable to patients with periodontitis and DM. Physicians and dentists utilize the clinical pathway to share medical and dental information in order to provide the optimal care for each patient. So far, this clinical pathway has been applied to the treatment of 50 patients. We analyzed clinical outcomes in 10 patients with the chief complaint of periodontal problems who had also been diagnosed with type 2 DM. After initial periodontal therapy and diabetes care, a significant improvement in the mean value of glycated hemoglobin and fasting plasma glucose was observed, accompanied by clinical resolution of periodontal parameters. Within the limitations of the present study, the results suggest that collaborative care between periodontists and physicians based on the clinical pathway is effective in glycemic control of patients with periodontitis and type 2 DM. This indicates the need for closer collaboration between medical and dental professionals in improving the management of these diseases.