To investigate the relationship of volatile sulphur compounds((VSC)levels in periodontal pockets with severity of periodontitis, and the impact of VSC on the result of initial periodontal therapy. Twenty-five patients with chronic periodontitis(CP)(13 males and 12 females with average age of 35) were included in this study. Clinical periodontal parameters, plaque index, probing depth(PD), attachment loss(AL), and bleeding on probing(BOP) were recorded before and 3 months after the initial therapy. VSC levels were measured with a portable monitor in a digital score ranging from 0.0 to 5.0. All of 5 054 sites for 840 teeth were included in this study. Before treatment the percentage of VSC-positive sites was 17.1%, 52.3% and 86.0% for shallow (PD<3 mm), moderate(PD 4-6 mm) and deep (PD>7 mm) pocket, respectively (P<0.001). In most VSC-positive sites the VSC levels were<1.0. Percentage of sites with a high VSC levels was significantly different among three groups (P<0.01). All clinical parameters in VSC-negative sites were reduced significantly following the initial therapy. The reduction of PD and AL in VSC-positive sites by treatment was less marked than that in VSC-negative sites. VSC in periodontal pockets may be a potential indicator for detecting severity of CP and a useful predictor for therapeutic success.