Introduction and objective. Toxoplasmosis is parasitic disease which has economic relevance for both veterinary and human medicine. In sheep, toxoplasmosis is a major cause of abortion and can thus cause reproductive problems. The current study aimed to determine the occurrence of anti-Toxoplasma gondii IgG antibodies in sheep from 13 districts of northern Poland and thereby obtain actual data about T. gondii seroprevalence in this population of animals. Materials and methods. Blood samples from 1,646 animals from 99 herds were collected, and an in-house enzymelinked immunosorbent assay (ELISA) based on native Toxoplasma lysate antigen (TLA) was used for serological testing. The diagnostic sensitivity of diagnostic test used in this study was 98.6%, and specificity 94.9% for the group of 113 sheep sera (74 seropositive and 39 seronegative) previously characterized by using an commercial agglutination test. Results. Antibodies against T. gondii were found in 921 (55.9%) of all tested animals. The percentage of infected sheep was the highest (67.6%) for older animals (>6 years), whereas for younger ones it was significantly lower (50.1% -57.2% for 1-5-year-old animals, respectively). Furthermore, a higher percentage of seropositive animals was noted among males (63%) than females (55.5%). The results also showed that the size of the herd is not a factor which may affect the seroprevalence of T. gondii infection in the examined population of sheep. Conclusion. The results of this study indicate that T. gondii infection in sheep from region of northern Poland is relatively high, and consumption of ovine meat and milk can be regarded as a significant source of infection for humans.