SUMMARYAn epidemiological investigation was conducted to identify risk factors related to hygiene and husbandry practices which determine the introduction of Campylobacter spp. into broiler chicken flocks. All 176 broiler farms in an area in southeastern Norway participated in the study. Each farm was represented by one flock selected at random during a one-year period. The flocks were examined for campylobacter colonization at slaughter, and the flock managers were subsequently interviewed about hygiene and husbandry practices. Campylobacter spp. were recovered from 32 (18%) of the flocks. The proportion of colonized flocks varied geographically and seasonally with a peak in the autumn. The following variables were found to be independently associated with an increased risk of campylobacter colonization using logistic regression analysis: (i) feeding the broilers undisinfected water (odds ratio (OR) = 3-42, P = 0045), (ii) tending other poultry prior to entering the broiler house (OR = 6-43, P = 0O007), (iii) tending pigs before entering the house (OR = 4-86, P = 0O037), (iv) geographic region (Hedmark versus 0stfold county) (OR = 2-91, P = 0-023, (v) season (autumn versus other seasons) (OR = 3*43, P = 0008). Presence of rats on the farm was associated with an increased risk, but this factor did not reach statistical significance (OR = 3-96, P = 0O083). Preventive measures should include disinfection of drinking water and strict hygienic routines when the farm workers enter the rearing room. The results indicate that disinfection of drinking water is the preventive measure most likely to have the greatest impact on the prevalence of campylobacter among broiler chicken flocks in the study area (population attributable fraction = 053).