Background/Aim. There is clear evidence on direct relationship between periodontal disease and diabetes mellitus. Many investigations point out greater prevalence and severity of periodontal disease among diabetic patients. During last decade, low level laser therapy has been used in periodontal therapy. It has biostimulative effect, accelerates wound healing, minimizes pain and swelling, and there is almost no contraindication for its usage. The aim of the paper was to investigate the efficiency of low level laser therapy as adjuvant tool in reduction of gingival inflammation in diabetic patients. Methods. The study incuded 150 participants divided into three groups: group I (50 participants with diabetes mellitus type 1 and periodontal disease), group II (50 participants with diabetes mellitus type 2 and periodontal disease), group III (nondiabetic participants with periodontal disease). Gingival health evaluation was done using gingival index Löe-Silness. Soft and hard deposits were removed, periodontal pockets cleaned and GaAlAs low level laser therapy (5 mW) applied five consecutive days. In each patient, low level laser therapy was not applied on the left side of the jaw in order to compare the effects of the applied therapy. After the first, third and fifth therapy and one month after the last visit gingival index was evaluated. Before the first and after the fifth therapy exfoliative cytology of gingiva was done and nuclei areal was analyzed morphometrically. Results. After all investigated periods, gingival index and nuclei areal were significantly decreased comparing to values before the therapy, at both jaw sides (p < 0.001). After the 1st, 3rd and 5th therapy, the t-test showed a significantly decreased gingival index at the lased side of jaw comparing to non-lased side. Conclusion. Low level laser therapy is efficient in gingival inflammation elimination and can be proposed as an adjuvant tool in basic periodontal therapy of diabetic patients.