Monobacterial necrotizing fasciitis is a rare form of soft tissue infection usually caused by the group A beta-hemolytic Streptococcus. Soft tissue infection is an uncommon clinical manifestation of invasive disease due to Streptococcus pneumoniae. We describe 3 cases of pneumococcal necrotizing fasciitis and explore potential pathogen-specific mechanisms of pathogenesis. The clinical characteristics of necrotizing fasciitis due to S. pneumoniae and group A beta-hemolytic Streptococcus appear to overlap. The similarities include predominant occurrence in elderly adults with underlying chronic illness, predilection for lower extremity infection, progression to toxic shock-like syndrome and a high case fatality rate. No DNA fragments corresponding to speA, speB or speC were amplified by PCR from the 3 pneumococcal isolates. Western immunoblot revealed no evidence of SpeA, SpeB or SpeC protein expression. Evaluation for protease production and cytotoxicity was unrevealing. The similar clinical presentation of pneumococcal necrotizing fasciitis to the disease caused by the group A beta-hemolytic Streptococcus has important therapeutic implications. The molecular mechanisms underlying the pathogenesis are unclear. Prospective population-based studies are required to define the epidemiology of this infection.