Studies investigating the eVect of visual illusions on saccadic eye movements have provided a wide variety of results. In this study, we test three factors that might explain this variability: the spatial predictability of the stimulus, the duration of the stimulus and the latency of the saccades. Participants made a saccade from one end of a Müller-Lyer Wgure to the other end. By changing the spatial predictability of the stimulus, we Wnd that the illusion has a clear eVect on saccades (16%) when the stimulus is at a highly predictable location. Even stronger eVects of the illusion are found when the stimulus location becomes more unpredictable (19-23%). Conversely, manipulating the duration of the stimulus fails to reveal a clear diVerence in illusion eVect. Finally, by computing the illusion eVect for diVerent saccadic latencies, we Wnd a maximum illusion eVect (about 30%) for very short latencies, which decreases by 7% with every 100 ms latency increase. We conclude that spatial predictability of the stimulus and saccadic latency inXuences the eVect of the Müller-Lyer illusion on saccades. © 2010 Springer-Verlag.