We presented 23 patients with necrotizing fasciitis (NF), 15 of whom had uncontrolled diabetes mellitus (DM), for risk factors, clinical signs, laboratory findings and prognosis during the period 1998 and 2006 in Istanbul. A hospital incidence of NF was 14.2/100,000 admissions. Other risk factors were obesity in 9 and recent surgical trauma in 10 patients. The mean age of the patients with DM was higher than that of the patients with non-DM (58.6+/-12.8 vs 43.0+/-17.2 years, p=0.028). The most frequently isolated microorganisms from tissue cultures were Escherichia coli, Klebsiella pneumoniae and Group A streptococci. Of the 23 patients, 9 (39%), of whom 8 had DM, died between 2 and 29 days after admission. The mortality rate and length of hospitalization were longer in diabetic patients than in others (p=0.02 and p=0.286, respectively). The mean blood glucose levels and HbA1C were higher in non-survival group than in survival group (195.6+/-41.5 vs 133.7+/-22.1 and 10.6 vs 7.4) (p=0.04, r=0.39 and p=0.03, r=0.50, respectively). In the univariate analysis, the hospitalization time (r=0.72), white blood cell count (r=0.52) and surgical debridement count (r=0.47) were found to be prognostic risk factors. Our results showed that NF is a very serious life-threatening disorder in especially diabetic patients with bad metabolic control.