Objective: To investigate retrospectively the incidence of Lyme boreliosis (LB) in the Primorsko Goranska Counti (PGC) in the period from 1 January 2018 to 31 December 2019. Materials and Methods: A retrospective analysis of the results of serodiagnostic methods of examination of 1843 blood serum samples of patients with epidemiological data on tick bites. The obtained results were compared with the data of the Croatian Institute for Public Health on reported cases of LB in the territory of the Republic of Croatia (RC) and PGC. Results: Of the 1,050 blood serum samples screened during 2018 for the presence of specific antibodies 34.1% had positive IgM antibodies to B. burgdorferi while in 2019 samples, specific antibodies were detected in 26.1% of the 793 samples. An increase in the number of positive samples was observed in the period from May to September. In 2018, the largest number of samples with positive IgM antibodies was in June (19.83%), and in 2019 in July (18.35%). The lowest number of positive samples in both observed years was recorded in January and December. In the period from 2009 to 2019 Croatian Institute for Public Health reported in the RC number of 510 ± 115.71 patients per year. In 2019, the number of reported cases in PGC amounted to 42.3% of the total number of cases reported in RC. Conclusions: A large number of patients with LB in the RC, as well in PGC, is a growing public health problem. This zoonosis transmitted by ticks of the genus Ixodes shows a seasonal character, but due to changes in climatic conditions, primarily milder winters, it is necessary to research the distribution of ticks in nature and implement preventive measures against infection.