A detailed magnetometer survey was carried out by Archaeological Surveys Ltd at Thornbury Castle in South Gloucestershire. The survey was requested within four areas, the West and East Court garden (Areas 1 and 2), the kitchen court and car park (Area 3) and the field to the north of the castle (Area 4). The East Court garden (Area 2) is part of the scheduled area which contains the buried remains of the demolished east wing of the 16th century castle and privy gardens. Area 3 contained numerous ferrous objects with associated high levels of magnetic disturbance precluding recorded survey. The results within Area 4, to the north of the castle, demonstrate the presence of a number of positive linear, rectilinear and discrete anomalies that appear to relate to ditch-like and pit-like features. Areas 1 and 2 in the West and East Court gardens contain widespread and very strongly magnetic disturbance from numerous buried services. A small number of very short positive and negative linear anomalies have been located within Areas 1 and 2, with some negative responses in the scheduled area. However the very limited size of these anomalies, coupled with the presence of such widespread magnetic disturbance and debris, means that while they may be associated with buried archaeological remains, they are incoherent and cannot be confidently interpreted.