Background: The relationship between diabetes mellitus and periodontal disease is well recognized as diabetes exacerbates periodontitis, while periodontal infections make blood sugar control in diabetic patients more difficult. Investigating different periodontal treatment modalities regarding their effects on blood sugar levels is essential. Objective: This investigation aimed to compare three different modalities of periodontal treatment, a SRP, b SRP with local antibiotic adjuncts, and c laser-assisted new periodontal attachment procedure in terms of improvement in blood sugar level through their effects in diabetic patients. Method: A prospective study was conducted at Al-Baha Dental Center, Saudi Arabia, on 75 diabetic patients with chronic periodontitis from 2009 to 2011. The patients were randomly assigned to one of the three treatment groups. The blood glucose levels were estimated in terms of HbA1c at baseline and 6-month intervals till 18 months post-treatment. Results: At the 18-month follow-up, the LANAP group exhibited the most substantial reduction in HbA1c levels, with an average decrease of 1.5% (from 8.5% to 7.0%, p<0.01), representing a 17.6% improvement. The SRP with the local antibiotic adjuncts group demonstrated a 1.2% reduction in HbA1c levels (from 8.4% to 7.2%, p<0.05), equivalent to a 14.3% improvement. The SRP group showed the most minor improvement, with a 0.9% decrease in HbA1c levels (from 8.3% to 7.4%, p<0.05), representing a 10.8% improvement. These results indicate that LANAP was significantly more effective in improving glycemic control than the other modalities. Conclusion: The laser-assisted new periodontal attachment procedure was found to be significantly superior to the other two modalities in reducing the blood glucose levels in periodontitis-diabetic cases, indicating that it could play a pivotal role in improving the perspective of achieving good blood sugar control as part of comprehensive periodontal therapy.