The main aim of this bachelor's thesis with the name – Chosen diseases of mallard Anas platyrhynchos is the analyse of diseases of mallard with a fact at contagious diseases. The mallard is sort of birds, which transcontinental seasonal migrational routes are ahead over Slovakia, so they are potential transporters of diseases. This work is concerned with choised diseases of mallard- viral, bacterial, parasitic and mycotic. An this in relation to others sorts of water birds and animals. In the work are defined diseases of birds too, which are incorporated into class zoonoses - infections in conjuction to people and animals. The work hint as potentional action climatic changes and factors which stereotyped abearance this migrational water birds are with this confronted. Therefore, due to the anthroposis of the biotope of water birds , the decline of the states and the reduction of the hunting interest in mallard, it would be desirable to further address this issue.