The development of fiber orientation in injection molding was manipulated by a special molding tool, the RCEM mold, which imposes a rotation action by one of the cavity surfaces during the filling stage. Center-gated disc moldings were produced from glass fiber reinforced polypropylene with different cavity rotation velocities, inducing distinct distributions and levels of fiber orientation. The morphologies of the moldings were characterized by optical and electronic microscopy. The through-thickness profiles of fiber orientation were assessed by means of the orientation tensor, and the relationship between the processing thermomechanical environment and the fiber orientation was established. At high rotation velocities, the resulting fiber orientation pattern is mainly controlled by the rotational motion, inducing a much more homogeneous through-the-thickness fiber orientation distribution, with a preferential alignment on the circumferential direction. POLYM. ENG. SCI., 48:395-404, 2008. (c) 2007 Society of Plastics Engineers.