Objective The aim of the study was to evaluate changes in the International Index of Erectile Dysfunction (IIEF) score following periodontal treatment in patients who had severe or moderate erectile dysfunction (ED) and chronic periodontitis (CP). Materials and methods The authors declare that they have no conflict of interest. The study population consisted of 120 patients with severe or moderate ED and CP. The treatment group (n = 60) comprised patients who received periodontal treatment, whereas the control group (n = 60) comprised patients who did not receive periodontal treatment. The clinical assessments were recorded at baseline, and at 1 month (R1) and 3 months (R2) after intervention for both groups. The periodontal examination involved assessment of the plaque index, bleeding on probing, probing depth and clinical attachment level. The IIEF questionnaire was used to assess the severity of ED. Results In the treatment group, the improvement in all clinical periodontal parameters was greater than that in the control group, at both R1 and R2 (p < 0.05). The increase in the IIEF scores of the treatment group at R2 was higher than that of the control group (p < 0.05), whereas the IIEF scores were similar for both groups at R1 (p > 0.05). Conclusion The findings of the study suggest that periodontal treatment can provide additional benefits in the improvement of ED. However, further studies are needed to understand the mechanisms of interaction between these diseases.