The first report on the use of peripheral prisms (p-prisms) for patients with left neglect and homonymous visual field defects (HVFDs).The purpose of this study was to investigate if patients with left hemispatial neglect and HVFDs benefit from p-prisms to expand the visual field and improve obstacle detection.Patients (24 with HVFDs, 10 of whom had left neglect) viewed an animated, virtual, shopping mall corridor and reported if they would have collided with a human obstacle that appeared at various offsets up to 13.5° from their simulated walking path. There were 40 obstacle presentations on each side, with and without p-prisms. No training with p-prisms was provided, and gaze was fixed at the center of expansion.Detection on the side of the HVFD improved significantly with p-prisms in both groups, from 26 to 92% in the left-neglect group and 43 to 98% in the non-neglect group (both P < .001). There was a tendency for greater improvement in the neglect patients with p-prisms. For collision judgments, both groups exhibited a large increase in perceived collisions on the side of the HVFD with the prisms (P < .001), with no difference between the groups (P = .93). Increased perceived collisions represent a wider perceived safety margin on the side of the HVFD.Within the controlled conditions of this simulated, collision judgment task, patients with left neglect responded well to initial application of p-prisms exhibiting improved detection and wider safety margins on the side of the HVFD that did not differ from non-neglect patients. Further study of p-prisms for neglect patients in free-gaze conditions after extended wear and in real-world mobility tasks is clearly warranted.