A newly developed computer-assisted conformation radiotherapy system is presented and its accuracy discussed in an experimental investigation and a clinical study. The system consists of a CT scanner, radiotherapy treatment planning system and linear accelerator. These systems are smoothly interconnected. Planning of multi-split conformation radiotherapy can be performed accurately and rapidly. Opening of the multi-split collimators was accurately controlled by computer on the basis of the treatment planning data. Dosage distributions in the irradiated body reconstructed using transit x-rays are also presented. As a simple back-projection method was used for calculation, the reconstructed dosage distribution resembling that of beam-focus radiography. Further investigation is required to complete this technique and to use it for the verification of radiotherapy treatment planning.