This review describes the microbiology, diagnosis and management of pericarditis due to anaerobic bacteria. The predominant anaerobes isolated from patients with pericarditis are Gram-negative bacilli (mostly Bacteroides fragilis group) as well as Peptostreptococcus, Clostridium, Fusobacterium, Bifidobacterium and Actinomyces spp. Anaerobic bacteria can be recovered from pericarditis resulting from the following mechanisms: (i) spread from a contiguous site of infection, either de novo or following surgery or trauma (pleuropulmonary, oesophageal fistula or perforation, and odontogenic); (ii) spread from a site of infection within the heart, most commonly from endocarditis; (iii) haematogenous infection; and (iv) direct inoculation resulting from a penetrating injury or cardiothoracic surgery. Anaerobic Gram-negative bacilli have increased their resistance to penicillins and other antimicrobial agents in the last two decades. Identification of pathogens and determination of their antimicrobial susceptibility and beta-lactamase production are essential for adequate selection of antibiotic therapy effective against these organisms.