The advanced single-slice rebinning algorithm (ASSR) is a highly accurate and efficient approximative algorithm for cone-beam spiral CT that (1) yields high image quality even at large cone angles, (2) makes use of available 2D backprojection algorithms/hardware and (3) allows for sequential data processing. It uses virtual R-planes (reconstruction planes) that are tilted to optimally fit 180 degree spiral segments. Along these R-planes data of a virtual 2D parallel scanner are synthesized via rebinning from the measured spiral cone-beam data. Reconstruction with 2D filtered backprojection yields the object cross-section in world coordinates [x, y, z(x, y)] which is resampled to carthesian coordinates (x, y, z) by z-filtering. Geometrical misalignments as well as any arbitrary detector geometry can be easily incorporated in the ASSR algorithm. ASSR, unlike other approximate algorithms, does not show severe cone-beam artifacts when going to larger cone angles. Even for scanners with a high number of detector rows, e.g. 64 rows, a high and isotropic z-resolution is achieved. In-plane resolution is determined by the 2D reconstruction filters which can be chosen as in 2D CT. Even in the case of only M equals 4 or M equals 8 simultaneously measured slices, ASSR may outperform standard z-interpolation algorithms such as 180 degree MFI. Due to its high efficiency and high image quality ASSR has the potential to be used for medical cone-beam CT.