Epidemiological studies have found that the estimated incidence of chronic constipation is up to 27% of the general population [1]. The gold standard to evaluate affected patients is the dynamic Entero-Colpo-Cysto-Defecography [2]. In clinical routine also 2D MR-defecography is performed, but only one to three 2D slices at a temporal footprint of about one second are acquired [2,3]. This leads to limitations in the detection of lateral localized pathologies. Therefore it was our aim to implement a dynamic 3D MR-defecography which covers a larger area and thereby gathers more detailed information on the anatomy during defecation.A radial 3D TrueFISP “Stack-of-Stars” [4] sequence was implemented (see Fig. 1 left). Density-weighting was implemented in z-direction to sample the center of the k-space more densely than the periphery (see Fig. 1 middle). Additionally, a view-sharing scheme was implemented to almost double the number of reconstructed time frames compared to the standard sampling scheme (see Fig. 1 right). The sequence was applied to the first 5 patients in an ongoing study. Each time frame featured a 3D block with seven partitions at a spatial resolution of 1.3x1.3x4.0mm³ to 2.0x2.0x6.0mm³ and a temporal footprint of 1.3s to 2.0s. Undersampled data (acceleration factor with respect to a fully sampled Cartesian sampling ≈ 6) were reconstructed by Compressed Sensing [5] applying a modified FISTA algorithm [6]. 3D dynamic MR-defecography was performed on a whole body 3T MR system (Siemens, MAGNETOM Prisma). The rectum of the patients was opacified with 200ml of sonographic gel. During the measurement the patient was asked to strain and squeeze several times and then to evacuate the rectum.After the compressed sensing reconstruction of all time frames, the defecation process can be visualized in all partitions of the 3D block. Figure 2 shows eight time frames from the time series of partition four of the dynamic 3D MR-defecography. It is clearly visualized how an anterior rectocele (red arrow) evolves during defecation. Figure 3 shows the seven acquired partitions of time frame four. Hence the lateral extent of the rectocele can be visualized as well.The presented images show that the proposed method allows for a dynamic 3D examination of the fast defecation process. The anatomical structure of the pelvic floor during defecation can be visualized and analyzed. Each 3D volume has a temporal footprint < 2s and the volume is updated due to the view-sharing with a rate of about 1s.Current 2D MR-defecography lacks information about lateral localized pathologies. Volumetric dynamic imaging of the defecation process allows for the visualization and interpretation of pelvic floor disorders and additionally allows for the detection of lateral localized pathologies.