Authors examine the influence of metal implants on the distribution of ionizing radiation in tissue. In vivo measurements in a patient are seldom possible. The risk can be assessed with sufficient accuracy on the basis of various experimental dosimetric methods, histological changes in the irradiated volume and the tolerance to the physical stress, published in the available literature. The analysis shows that the risk of significant dose inhomogeneity or the treatment toxicity is minimal if mentioned principles are adhered to. Radiotherapy indications and dosage should not be markedly changed on the basis of the presence of metal in the irradiated volume.