Lyme borreliosis, caused by spirochaetes of the Borrelia burgdorferi sensu lato genospecies complex, is the most commonly reported tick-borne infection in Europe including Estonia. In clinical practice, especially in areas rich in ticks, the diagnosis of LB and the interpretation of serological tests is often challenging. The new European case definitions of Lyme borreliosis emphasise recognition of clinical manifestations supported by relevant laboratory criteria, which should be used in a clinical setting. When interpreting the results of serological tests one should bear in mind that, first, they are supportive to clinical findings; second, that in areas with high prevalence of ticks the background antibody levels are high and that immediately after acquiring the infection antibody levels are either zero or very low. With appropriate antibacterial management the outcome of Lyme borrelliosis is usually good. There is very little evidence of chronic Lyme borrelliosis and/or post Lyme syndrome.