The aim of this study was to identify the factors determining the incidence of Lyme borreliosis (LB) in southwestern Poland by estimating the prevalence of B. burgdorferi s. 1. in I. ricinus, and to analyze the temporal abundance of ticks in relation to epidemiological data on LB incidence. Host-seeking ticks collected in 2011 in four districts in southwestern Poland were examined by nested PCR for the presence of B. burgdorferi s.l. In total, 2,507 host-seeking I. ricinus were collected. The temporal abundance of ticks varied between districts. The minimal infection rates with B. burgdorferi s.l. were 11.5% for nymphs and 37.7% for adults. There were no statistical differences in the level of infection between districts either for nymphs or for adults. Five different genospecies were identified within the B. burgdorferi s.l. complex: B. garinii, B. afzelii, B. lusitaniae, B. valasiana, and B. burgdorferi s.s., and additionally B. miyamotoi. Our results point to a relationship between tick temporal abundance and LB incidence both for adults and nymphs. The high abundance of ticks is positively correlated with the number of LB cases in humans. The tick's abundance may be considered as a major factor in determining the LB risk in southwestern Poland.