Biosecurity in livestock farming includes all measures preventing pathogen introduction onto a farm (external biosecurity) and pathogen transmission on the farm itself (internal biosecurity). An important risk factor for the dissemination of infectious diseases are specialised external persons working on numerous farms, such as professional hoof trimmers in Switzerland. In the present study, 49 hoof trimmers, participating in the Swiss claw health programme and working as professionals, were questioned regarding their biosecurity measures and observed by two veterinarians during hoof trimming in order to assess the implementation of biosecurity measures by hoof trimmers. Data were processed using a scoring system, in which points were allocated to the different working methods taking into account their assumed transmission potential for infectious diseases such as digital dermatitis (DD) and Salmonellosis. The working method, which complied with the ideal biosecurity measure, was always given a whole point, whereas less optimal working methods were only given an intermediate value or no point. The scoring system helped identify precisely the strengths and weaknesses of the hoof trimmers in terms of biosecurity. The level of implementation of biosecurity measures by hoof trimmers was overall quite low (53 %=average of the overall biosecurity scores of the 49 hoof trimmers). Hoof trimmers which attended specialised training courses tended to have a higher level of implementation of biosecurity measures. The answers given by the hoof trimmers and the observations made by the veterinarians were compared, whereby it was found that hoof trimmers generally evaluated themselves better in regard to biosecurity than veterinarians assessed them. In summary and based on the results of this study, the dissemination of pathogens, such as DD associated treponemes and salmonella is possible during hoof trimming performed by external persons working on numerous farms. Thus, future training and continuing education courses should place emphasis on biosecurity.