A 2-month prospective study of Clostridium difficile infections was conducted in 38 hospitals from 14 different European countries in order to obtain an overview of the phenotypic and genotypic features of clinical isolates of C. difficile during 2005. Of 411 isolates from diarrhoeagenic patients with suspected C. difficile-associated diarrhoea (CDAD), 354 were toxigenic, of which 86 (24.3%) were toxin-variant strains. Major toxinotypes included toxinotypes 0 (n = 268), V (n = 28), VIII (n = 22) and III (n = 25). MICs of metronidazole, vancomycin, erythromycin, clindamycin, moxifloxacin and tetracycline were determined using the Etest method. All the toxigenic strains were fully-susceptible to metronidazole and vancomycin. Resistance to erythromycin, clindamycin, tetracycline and moxifloxacin was found in 44.4%, 46.1%, 9.2% and 37.5% of the isolates, respectively. Sixty-six different PCR ribotypes were characterised, with the 027 epidemic strain accounting for 6.2% of isolates. This strain was positive for binary toxin genes, had an 18-bp deletion in the tcdC gene, and was resistant to both erythromycin and moxifloxacin. The mean incidence of CDAD was 2.45 cases/10 000 patient-days, but this figure varied widely among the participating hospitals. Patients infected with the 027 strain were more likely to have a severe disease (OR 3.29, 95% CI 1.19-9.16, p 0.008) and to have been specifically treated with metronidazole or vancomycin (OR 7.46, 95% CI 1.02-154, p 0.02). Ongoing epidemiological surveillance of cases of CDAD, with periodic characterisation of the strains involved, is required to detect clustering of cases in time and space and to monitor the emergence of specific highly virulent clones.