To evaluate the clinical, bacteriologic, and genetic relatedness between invasive and non-invasive infections caused by group A Streptococcus (GAS), we retrospectively analyzed the GAS isolates in our hospital from the past decade. A total of 70 GAS-infected cases were enrolled in our study from the period 1993 to 2002. Twenty one cases had invasive disease, and 49 were non-invasive. Their medical records were reviewed, and demographic data were collected for analysis. Antimicrobial susceptibility testing was conducted according to the National Committee for Clinical Laboratory Standards for Streptococcus spp. Isolates were subjected to chromosomal SmaI (Invitrogen) digestion of pulsed-field gel electrophoresis (PFGE), and emm typing was also performed. The mean age of the invasive group was 41.1 +/- 22.4 years compared with 13.0 +/- 16.6 years for the non-invasive group (p<0.05). Eighty one percent of the invasive group had underlying diseases. Diabetes and malignancy were the 2 most common medical conditions. All isolates were susceptible to penicillin. The resistance rate was 42.8% and 55.1% for erythromycin in the invasive and non-invasive groups, respectively. A total of 51 different PFGE types were identified among the GAS isolates without particular genotypes. Serotype M12 was the most common one (28.4%), followed by M4 (19.4%). Our study demonstrated that the patients in the invasive group were older, with more underlying diseases, and with a higher mortality rate. Antimicrobial susceptibility of the isolates was the same in both groups. There was no epidemic strain, nor did PFGE reveal a more invasive clone.