OBJECTIVE To implement 3D-reconstruction of CT and MR data by a standard MS-DOS personal computer. METHODS User-specific software has been developed for the 3D-reconstruction and quantitative evaluation of hard and soft tissues of the skull. RESULTS The software displays a 3D-reconstruction and secondary reformatted vertical sections within 4-30 s on the monitor. The 3D-structures can be evaluated quantitatively with a freely-superimposable grid. Distances or angles between two landmarks can be measured directly. Various tools for the simulation of surgical treatment are available. CONCLUSIONS Gross skeletal and soft-tissue malformations, topographical relations and the degree of asymmetry of severe maxillofacial deformities can be evaluated in more detail. Access to a readily available low-cost computer system for 3D-evaluation of the head will enable a larger number of clinicians to use 3D-methods in diagnosis and treatment planning. The off-line computing system permits a higher of flexibility independent of any computing centre.