A survey to estimate the seroprevalence of ovine and caprine brucellosis was conducted in the region of Tras-os-Montes e Alto Douro, Northeast of Portugal. In total, 278,097 small ruminants and 5,466 flocks from 13 Livestock Farmers Organizations (OPP's) were analysed. Four hundred and eighty seven (8.9%) flocks had one or more serologically positive animals with values ranging between 8.2% and 9.7%. The individual seroprevalence was 0.44% (CI 95% 0.40-0.48%). There were significant differences in seroprevalence rates among herd sizes, species, constitution of herd, production's type and OPP. Based on the results of this survey, a small percentage of animals and a high percentage of flocks in the Northeast of Portugal were serologically positive. Considering the paucity of epidemiological reports on brucellosis in the Northeast of Portugal the information on seroprevalence provided in this study is necessary to define control measures for brucellosis in the area.