People who suffer from acrophobia fear any situation that involves heights. Several virtual reality systems have been presented to treat this problem. This paper presents a comparison study of the levels of presence and anxiety in an acrophobic environment that is viewed using a computer automatic virtual environment (CAVE) and a head-mounted display (HMD). In this environment, the floor fell away and the walls rose up. To determine whether either of the two visualization systems induced a greater sense of presence/anxiety in non-phobic users, an experiment comparing the two visualization systems was carried out. Twenty-five participants took part in this study. After using each visualization system (HMD or CAVE), the participants were asked to fill out an adapted Slater et al. questionnaire (Slater, Usoh, & Steed, 1994), and a Student t test was applied to the data obtained. The CAVE induces a high level of presence in users. The mean score was 5.01 (where 7 is the maximum value), which was higher than the score obtained using the HMD which was 3.59. The Student t test indicates that there are significant statistical differences. The level of anxiety was also examined at different times during the experiment. The results indicate that both visualization systems provoke anxiety, but that the CAVE provokes more anxiety than the HMD. The animation in which the floor falls away is the one that provoked the most anxiety. The results from the correlation between the anxiety and the level of presence at the three times indicated a significant correlation between the two measures.