To counter user disorientation and cognitive overload, hypertext environments often incorporate navigational aids in the form of graphical overviews of the hypertext structure. The aim of the present experimental investigation of learning in hypertext environments was to examine the impact of such graphical overviews on learning achievement in conjunction with the respective influence of individual learner variables. In a sample of N = 82 students working on a hierarchically structured hypertext about the psychology of memory, how domain-specific prior knowledge and the self-concept of computer-related ability affect perceived disorientation and learning outcomes as a function of access to a navigational aid was tested. Participants provided with a graphical overview experienced somewhat less disorientation, particularly those with high prior knowledge. A high computer-related self-concept also helped to curb disorientation. Both prior knowledge and computer-related self-concept proved to be significant predictors of complex learning achievement (i.e., the acquisition of structural knowledge). Participants with high prior knowledge, a high self-concept, and access to the graphical overview achieved better retention scores (i.e., acquired more purely factual knowledge). (Contains 3 tables and 2 figures.)