Variations in the shape and size of the sigmoid sulcus were investigated in 561 temporal bones (438 isolated temporal bones, 49 skull bases and 25 half skull bases) and measurements of related structures were made. Right-left differences were analysed. The sigmoid sulcus was significantly wider (12 mm) and longer (38 mm) in the skull bases, while no differences were observed in the isolated temporal bones. The distance from the most prominent point of the mastoid process to the Frankfort horizontal plane (FHP) was 33 mm; no right-left difference was found. The distance from the genu of the sigmoid sulcus to the external acoustic meatus was 24.06 mm on the right side and 24.74 mm on the left side and this difference is significant, being considerably longer on the left side. The jugular foramen diameter was 7.8 mm; no right-left-difference was observed. The relationship of the mastoid air cells to the sulcus was analysed and air cells were found just behind the sulcus in 66% and behind and posterior to the sulcus in 5% of temporal bones.