OBJECTIVE: Our objective was to assess the effect of orthopedic metallic prostheses on radiation dose associated with MDCT using z-axis automatic tube-current modulation and a fixed tube current in a phantom and patient study. CONCLUSION: Z-modulation is associated with a 34.1% increase in the mean tube current-time product and no change in the extent of streak artifacts in patients with a metallic prosthesis, compared with patients without a prosthesis. However, compared with the fixed-tube-current technique, z-modulation is associated with a 28.9% decrease in the mean tube current-time product.