In order to estimate the risk of contracting Lyme disease in the forestareas of north-western Poland, PCR-based studies were carried out on 6,817 Ixodes ricinus ticks for infectionby the spirochaete B. burgdorferi sensu lato (s.l.). The studies were performed using the primers forthe fla gene, conserved for all European genospecies of B. burgdorferi s.l. Based on the incidence ofB. burgdorferi s.l. DNA in I. ricinus ticks at eight sampling sites during 1998-2001, it may be concludedthat a risk of contracting Lyme disease is present in the forest areas of north-western Poland. The highestrisk of infection (9.4 % of infected ticks) is posed by human contact with female I. ricinus, and therisk is higher in late spring and early summer than in late summer and early autumn. The north-westernpart of Poland is an endemic region for B. burgdorferi s.l.