Anaerobic bacteria play important roles in the pathogenesis of human periodontitis. This study examined the relationship between a potentially new periodontopathic bacterium Dialister pneumosintes and periodontal disease. A total of 73 women and 62 men aged 18 to 86 years participated in the study. Using a 16S rRNA polymerase chain reaction identification method, the presence of D. pneumosintes was determined in paper‐point samples from periodontal pockets of 105 periodontitis and 30 gingivitis patients. D. pneumosintes was detected in 83% of patients having severe periodontitis and in 19% of patients having slight periodontitis. We suggest adding D. pneumosintes to the group of suspected periodontal pathogens.