BACKGROUND AND OBJECTIVE: Melatonin is synthesized naturally by pineal gland and responsible for regulation of sleep/waking cycle. It showed appreciated anti-inflammatory and antioxidant properties. The aim of this randomized clinical trial (RCT) was to assess the additive effect of melatonin supplementation in insomniac individuals with generalized chronic periodontitis (gCP) after scaling and root planing (SRP). MATERIAL AND METHODS: Seventy-four gCP patients with primary insomnia participated in this 6-month RCT and randomized into two groups. Melatonin group included 38 patients who were subjected to SRP with a 2-month regimen of 10 mg oral melatonin capsule once daily before bedtime. In the control group, SRP was performed for 36 participants provided with matching placebo capsules. The primary treatment outcome was the measurement of clinical attachment level gain (CAL gain) after 3 and 6 months of therapy, whereas the measurements of pocket depth reduction (PD reduction), bleeding on probing (BOP %), and the changes in salivary TNF-α levels and Athens insomnia scale (AIS) scores represented the secondary endpoints. RESULTS: Melatonin group showed significantly greater CAL gain and PD reduction measurements compared to the control group at 3 and 6 months of therapy, P < 0.01. Likewise, salivary TNF-α levels and AIS scores were significantly lower in the melatonin group compared to placebo group. BOP% improved significantly in both groups without any difference. However, salivary TNF-α levels exhibited no correlation with other clinical variables in both melatonin and placebo groups. CONCLUSION: Daily dietary 10 mg of melatonin supplementation might serve as a viable adjunct to SRP that yielded significantly greater CAL gain and PD reduction and lower salivary TNF-α levels and AIS scores in gCP patients with primary insomnia.