The purpose of the study was to assess the incidence of Borrelia burgdorferi antibodies and clinical forms of Lyme borreliosis among forestry workers in north-eastern Poland. The group studied consisted of 1,466 persons (297 women and 1,169 men), aged 20-70 years. In 439 (23.81%) persons the presence of B. burgdorferi antibodies was detected in serum, in 271 (18.49%) persons active Lyme borreliosis was diagnosed and 78 (5.32%) persons were carriers of B. burgdorferi antibodies. Arthritis (43.84%) and neuroborreliosis (32.95%) were found to be the most common forms of borreliosis.