This study was conducted in order to determine the prevalence of Borrelia burgdorferi sensu lato in Ixodes ricinus ticks, which are the primary vectors of this spirochete, as well as to investigate the effect of 1. ricinus population density on the prevalence of B. burgdorferi s.l. Ticks were collected by blanket dragging in 13 different forest regions of Sinop, Turkey, and its vicinity. Ticks were identified under a stereo microscope. 1. ricinus (n = 334), 1. hexagonus (n = 5), Rhipicephalus spp. in = 10), Dermacentor spp. in = 7), and Hyalomma spp. (n = 5) were collected. Direct immunofluorescence was used to detect B. burgdorferi in collected ticks. B. burgdorferi was detected in 15.9% (53/334) of the 1. ricinus specimens examined. This spirochete was not detected in 1. hexagonus, Rhipicephalus spp., Dermacentorspp., or Hyalomma spp. The prevalence of B. burgdorferi infection in 1. ricinus tended to be higher in regions where l. ricinus was most abundant.