Aim: The present study proposes an assessment of the clinical effects on periodontal level generated by the adjunctive periodontal therapy with sub-antimicrobial doses of doxycycline in patients with chronic periodontitis and osteoporosis. Materials and Methods: The study group comprised 26 patients with chronic periodontitis and osteoporosis, divided in the study group (classical periodontal debridement and sub-antimicrobial doses of doxycycline for 3 months) and the control group (classical debridement only). We analyzed the periodontal parameters (probing depth, clinical attachment level, PBI and PI indices) at baseline, in the last day of medication and at 3 months after the drug therapy. Results and Discussion: The reduction of the moderate and profound pockets was higher for the group with drug adjunctive therapy. The sites with an initial depth of 0-3mm in the study group presented also a slight attachment gain. Conclusions: The therapy with sub-antimicrobial doses of doxycycline generated significant clinical improvement in patients with chronic periodontitis and osteoporosis, an improvement which can reduce the necessity of surgical procedures.