Introduction. During feeding, the tick sucks blood from the host along with the pathogens that are in the blood, simultaneously exchanging its own pathogens with the host. Humans can also be a host. It is important to understand the most typical circumstances in which people might become infected with Borrelia burgdorferi. This knowledge will help to prepare health education programmes aimed at the prevention of Lyme disease and other tick-borne diseases. Objective. The aim of the study was to determine the percentage of ticks infected with Borrelia burgdorferi sensu lato, depending on the circumstances of getting bitten. Materials and method. The research material consisted of ticks acquired from people who had been bitten, and questionnaires completed by these people. 510 ticks were acquired from 257 females and 253 males. Following delivery of a tick for testing, the stage of its development was determined and a molecular assay of Borrelia burgdorferi DNA performed. Results. A positive result of the nested-PCR test was obtained in 78 ticks, which represents 15.30% of all ticks. The infected ticks were collected from male (41 ticks – 52.56%) and female subjects (37 ticks – 47.44%). The biggest number of infected ticks were collected in autumn (54 ticks – 69.23%) and from people who had been into forests (44 ticks – 56.41%). Among the people from whom the infected ticks were acquired, the dominating group included persons over 16 years of age (53 persons – 67.95%) and children aged 0–5 years (16 persons – 20.51%). One in four infected ticks were acquired from the southwestern (20 ticks – 25.64%) and eastern regions of Poland (21 ticks – 26.92%). Conclusion. Infestation of ticks infected with Lyme disease spirochete in this study proved to be variable and depend on the season, the area of tick attack and the region in Poland. The results of the study clearly show that ticks infected with Borrelia burgdorferi inhabit all regions of Poland. The results are consistent with National Institute of Hygiene data which indicates that Lyme disease cases are recorded in all regions of Poland.