The present invention relates to a method for assisting with percutaneous interventions, wherein 2D x-ray images of an object region are recorded before the intervention using a C-arm x-ray system or a robot-based x-ray system at different projection angles and 3D x-ray image data of the object region is reconstructed from the 2D x-ray recordings. One or more 2D or 3D ultrasound images are recorded before and/or during the intervention using an external ultrasound system and registered with the 3D image data. The 2D or 3D ultrasound images are then overlaid with the 3D image data record or a target region segmented therefrom or displayed next to one another in the same perspective. The method allows a puncture or biopsy to be monitored with a low level of radiation.