Fresnel prisms improve visual perception in stroke patients with homonymous hemianopia or unilateral visual neglect. We randomly assigned 39 patients with stroke and homonymous hemianopia or unilateral visual neglect to treatment with 15-diopter plastic press-on Fresnel prisms (n = 18) or to serve as controls (n = 21). Baseline evaluations of visual perception and activities-of-daily-living (ADL) function were similar for both groups. After 4 weeks, the prism-treated group performed significantly better than controls on the following: (1) Motor Free Visual Perception Test; (2) Line Bisection Task; (3) Line Cancellation Task; (4) Harrington Flocks Visual Field Screener; and (5) Tangent Screen Examination. There was no significant difference in Barthel ADL assessment at 4 weeks. Thus, treatment with 15-diopter Fresnel prisms improves visual perception test scores but not ADL function in stroke patients with homonymous hemianopia or unilateral visual neglect. 