Appropriate application of the Nd: YAG laser has been shown to reduce bacteria associated with periodontal pockets and improves the health of the diseased periodontal pocket tissue [1&2]. The objective of this in-vivo study is to investigate the effects of the 100 micro-second pulsed width (length) Nd: YAG laser on bacteria and pocket depth associated with periodontal disease. An Nd: YAG laser (Fidelias, FOTONA, Slovnia: 2 Watts and 10 Hz, 320 Micrometer beam diameter with a pulse duration of 100 micro-seconds) was used to irradiate the gingival pockets after the removal of calculus and appropriate root planning with hand instruments. Fifty-two teeth from six patients diagnosed with chronic periodontitis were used in this study. The samples were divided into two groups (control and experimental). All teeth were treated by normal hand instrumentation but in the experimental group the Nd: YAG laser was used to irradiate the pocket following hand instrumentation. Bacteria cultures were obtained from the gingival pockets prior to treatment, immediately after treatment, one and two months after treatment.The laser group of teeth demonstrated a significant reduction in bacteria, Probing Index (PI) and Bleeding Index (BI) compared to the control group of teeth.