In four years period - from 1994 to 1997 twelve broiler breeder flocks in north east part of Slovenia showed clinical sings of swollen head syndrome. The disease occurred at the beginning of production period. The clinical sings was much more severe in females than in males. Morbidity was high, up to 100%, mortality was low ( 0 - 6%). Although drops in egg production were recorded, at the end of the laying period an average egg production per hen in affected flocks was only slightly lower compared to apparently healthy flocks. Antibodies to turkey rhinotracheitis virus, detected by commercial ELISA test, were present in all affected flocks (12) and also in 9 apparently healthy flocks. Increasing of positive reactions during three years was observed.