This is a report on clinical experience had with 17 patients presenting necrotizing fasciitis--a complication ever more frequently encountered. The case material is distributed in two group differing by origin and clinical course of the complication. In group one (n = 11) it is a matter of postoperative development of postoperative complication, consistent with the classical "per continuitatem" and "per contiguitatem" mechanisms, while in group two (n = 6) the process originates, evolves and speads within the retroperitoneal space proper. Comprehensive microbiological examinations performed in 13 cases show that in either group different microorganisms are identified. In group one aerobic-anaerobic mixed infection is documented in all patients, with predominance of Enterobacteroidaceae among aerobic ones. In group two, anaerobic bacterial species, mainly Clostridium sp, prevail in all the isolates. The clinical study points to a substantial difference in the time of septic complication occurrence, as well as between the clinical picture of the two species. Accordingly, the final results are radically different--in group one survivorship amounts to 62.6%, whereas in group two--to 16.6% only.