The invention relates to a method and a device for the three-dimensional reconstruction of the flow conditions in a vascular system (3), in which, in a first phase after the beginning of a contrast-medium injection, X-ray projection pictures are produced from the same direction (A) at a high picture-taking rate in order to observe the inflow of the contrast medium. When the contrast medium fills the vascular system (3), a rotation of the Xray device (1) takes place during which projection pictures are produced at a lower picture taking rate and/or at a lower radiation dose, from which pictures the three-dimensional structure of the vascular tree can be reconstructed. Optionally, at the end of the rotation, projection pictures may again be taken from a fixed direction that observe the drainage of the contrast medium from the vascular system (3).