Body mass and surface areas are important in several aspects for an organism living today. Therefore, mass and surface determinations for extinct dinosaurs could be important for paleo-biological aspects as well. Based on photogrammetrical measurement the body mass and body surface area of the Late Jurassic <i>Brachiosaurus brancai</i> Janensch, 1914 from Tendaguru (East Africa), a skeleton mounted and exhibited at the Museum of Natural History in Berlin (Germany), has been re-evaluated. We determined for a slim type of 3D reconstruction of <i>Brachiosaurus brancai</i> a total volume of 47.9 m³ which represents, assuming a mean tissue density of 0.8 kg per 1,000 cm³, a total body mass of 38,000 kg. The volume distributions from the head to the tail were as follows: 0.2 m³ for the head, neck 7.3 m³, fore limbs 2.9 m³, hind limbs 2.6 m³, thoracic-abdominal cavity 32.4 m³, tail 2.2 m³. The total body surface area was calculated to be 119.1 m², specifically 1.5 m² for the head, 26 m² neck, fore limbs 18.8 m², hind limbs 16.4 m², 44.2 m² thoracic-abdominal cavity, and finally the tail 12.2 m². Finally, allometric equations were used to estimate presumable organ sizes of this extinct dinosaur and to test whether their dimensions really fit into the thoracic and abdominal cavity of <i>Brachiosaurus brancai</i> if a slim body shape of this sauropod is assumed. <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.200700011" target="_blank">10.1002/mmng.200700011</a>