The posterior peri-Sylvian area is the most highly lateralized part of the human brain due to its specialised role in language. Currently, there is no clearly defined posterior boundary of the temporal lobe which takes account of language lateralization and which can be reliably determined radiologically. However, there have been a number of recent advances in magnetic resonance technology including volume visualisation techniques which have as their goal the realistic three-dimensional representation of the brain which is acquired in two-dimensional slices. These have enabled the identification of precise macroanatomical and cytoarchitectural boundaries from which an efficient and reproducible posterior limit may be demarcated. Such limit standardisation is important for volumetric investigations of both neurological and psychiatric disease. Magnetic resonance imaging (MRI) scans of 20 normal subjects (10 male and 10 female), aged between 18 and 42 years, were acquired as part of a study of normal temporal lobe volume variation. In order to demonstrate the method of posterior limit placement, a thin slice (1.5 mm) 3D spoiled gradient magnetic resonance image of the brain of a 30 year-old right-handed male, without neurological disease, was acquired on a 1.5 tesla GE magnetic resonance machine. The data set was transferred via network to the hard disk of a 166 MHz Pentium processor PC. A software package called MEASURE allowed reformation of the data set in all three orthogonal planes. Then, using a high resolution algorithm, the brain was aligned along the newly proposed posterior plane which runs from the limit of the Sylvian fissure, identified on a 3D rendering, to the posterior/inferior splenium. It is hoped that this procedure will be utilised as a standard method for radiological determination of the limit of the posterior temporal lobe in order to allow volumetric measurements of this structure to be compared in a meaningful way.