Lyme borreliosis is the most commonly reported tick-transmitted infectious disease in the northern hemisphere in humans. Certain diseases are associated with Lyme borreliosis in the dog as well, but only intermittent lameness with articular swelling, lymphadenomegaly, fever, and anorexia were experimentally documented. Lyme borreliosis is considered an over diagnosed disease. The term "Lyme nephritis" was introduced for dogs with characteristic renal lesions and typical clinical signs, in which antibodies against Borrelia burgdorferi were found. Different studies have been aimed at showing a relation between renal disease and B. burgdorferi infection; however, this was not possible until now. Reasons for the uncertainty of the effects of B. burgdorferi in the dog are the high prevalence of circulating antibodies, the unspecific clinical picture and the inaccuracy of serologic tests.