Objective: To evaluate the evidence on three-dimensional immediate effects of rapid maxillary expansion (RME) treatment on growing patients as assessed by computed tomography/cone beam computed tomography (CT/CBCT) imaging. Materials and Methods: The published literature was searched through the PubMed, Embase, and Cochrane Library electronic databases from January 1966 to December 2012. The inclusion criteria consisted of randomized controlled trials, prospective controlled studies, and prospective case-series. Two reviewers extracted the data independently and assessed the quality of the studies. Results: The search strategy resulted in 73 abstracts or full-text articles, of which 10 met the inclusion criteria. When treating posterior crossbites with a RME device, the existing evidence points out that the midpalatal suture opening is around 20%-50% of the total screw expansion. There seems to be no consistent evidence on whether the midpalatal sutural opening is parallel or triangular. The effect on the nasal cavity dimensions after RME seems to be apparent and indicates an enlargement between 17% and 33% of the total screw expansion. Circummaxillary sutures, particularly the zygomaticomaxillary and frontomaxillary sutures and also spheno-occipital synchondrosis, appear to be affected by the maxillary expansion. Overall, however, the changes were small and the evidence not conclusive. Conclusions: CT imaging proved to be a useful tool for assessment of treatment effects in all three dimensions. The majority of the articles were judged to be of low quality, and therefore, no evidence-based conclusions could to be drawn from these studies.