In 2005, human Campylobacter (C) infections accounted for the majority of notifyable bacterial gastrointestinal infections in Germany Consumption and handling of contaminated poultry meat is regarded as one of the major sources of human Campylobacter infection. To investigate the prevalence of Campylobacter spp. in German broiler flocks, a monitoring project was established in May 2004 by the Federal Institute for Risk Assessment in collaboration with selected Lander (States). In the first phase from May 2004 to April 2005 representative data were obtained about Campylobacter prevalence in broiler flocks. Fourteen large poultry slaughterhouses were included. All breeders who submitted their birds to these slaughterhouses were sampled twice per year. Caeca were obtained during slaughter and faecal material was used for isolation and identification of Campylobacter spp. Additionally, antibiotic resistance of the isolates was tested. Campylobacter spp. were detected in 532 (40%) of the 1331 investigated broiler flocks. A distinct seasonality - with the highest prevalences in the summer months - was notified. Out of the isolated strains, 268 (58.5%) were identified as C. jejuni and 190 (41.5%) as C. coli. Of the 433 isolates tested for antibiotic resistance, 0.4% of C. jejuni and 8.1% of C. coli were resistant to erythromycin, while 41.3% and 60.2% of the isolates were resistant to ciprofloxacin, respectively. All tested isolates were sensitive to gentamicin.