Group A streptococcus (GAS) has been described as an emerging cause of severe invasive infections. A retrospective hospital-based study was conducted, including GAS isolates causing invasive or non-invasive infections from January 1999 to June 2003 in Barcelona. Demographic and clinical information on the invasive cases was obtained from medical files. GAS isolates collected from 27 patients with invasive infections and 99 patients with non-invasive infections were characterized by emm type and subtype, superantigen (SAg) gene profile (speA-C, speF-J, speL, speM, ssa and smeZ), allelic variants of speA and smeZ genes, antibiotic susceptibility and genetic resistance determinants. The most prevalent emm type was emm1 (17.5%), followed by emm3 (8.7%), emm4 (8.7%), emm12 (7.1%) and emm28 (7.1%). The smeZ allele and SAg gene profiles were closely associated with the emm type. The speA2, speA3 and speA4 alleles were found in emm1, emm3 and emm6 isolates, respectively. Overall, 27.8, 25.4 and 11.9% of isolates were resistant to erythromycin, tetracycline or both agents, respectively. Reduced susceptibility to ciprofloxacin and levofloxacin (MIC 2-4 μg ml-1) was found in 3.2% of isolates. mef(A)-positive emm types 4, 12 and 75, and erm(B)-positive emm types 11 and 25 were responsible for up to 80% of the erythromycin-resistant isolates. No significant differences in emm-type distribution, SAg gene profile or resistance rates were found between invasive and non-invasive isolates. The SAg and antibiotic resistance genes appeared to be associated with the emm type and were independent of the disease type. © 2006 SGM.