BACKGROUND Aspiration pneumonia has a high recurrence rate, and oral care by dentists has been reported to be effective in preventing the onset of aspiration pneumonia; however, this has not been evaluated using prospective studies. Therefore, we conducted a prospective study to evaluate the effectiveness of professional oral care by dentists in reducing the recurrence of aspiration pneumonia in older adult patients. METHODS This was a prospective cohort study to evaluate a dental oral care intervention with a historical control. It was conducted at a single-center regional core hospital in Japan that serves a large number of patients aged > 80 years. Patients who were hospitalized for aspiration pneumonia were included in this study. The historical control group received oral care from nurses as usual and was followed retrospectively for 1 year. The dentist oral care group received weekly professional oral care from a dentist and was followed prospectively for 1 year. A Kaplan–Meier analysis was used to evaluate the timing of recurrent aspiration pneumonia or death events. A Cox proportional hazards model was used to obtain a hazard ratio and to determine the 95% confidence intervals. RESULTS There were 91 participants in the dentist oral care group and 94 in the control group. The mean age of participants in this study was 85 years, and 75 (40.5%) were women. The recurrence rate was 27.5% in the dentist oral care group and 44.7% in the control group, a statistically significant difference (P = 0.005). Dentist oral care reduced the risk of recurrence of aspiration pneumonia by approximately 50% (adjusted hazard ratio, 0.465; 95% confidence interval, 0.278–0.78). CONCLUSIONS Dentist-provided professional oral care was associated with a lower rate of aspiration pneumonia recurrence than nurse-provided conventional oral care.