The frequency of Johne's disease in cattle in the South West England was estimated from data collected by telephone interview of veterinarians and farmers. The response rate was 81.6%. Disease frequency was expressed as the proportion of farms with clinical disease and the cumulative incidence within infected herds. The proportion of farms affected was 1.0% and the cumulative incidence on those farms was 1.9% per year. Similar values were obtained when diagnosis by fecal examination, post-mortem examination and histology were taken into consideration; 0.9% of farms were affected and the cumulative incidence in infected herds was 2.0% per year. The survey was validated against three external reference points. There was good agreement between vaccine use and MAFF records, and the total number of holdings and census data. When responses of veterinarians were compared with those of farmers there was also good agreement on vaccine use (kappa=77.8%), the number of cases reported in the last year of diagnosis (r=0.78) and the total number of cattle within herds (r=0.75). However the results suggest that the total number of cattle holdings was overestimated and consequently the proportion of farms affected may have been underestimated.