Techniques for rendering 3-D medical data are described. They consist of (1) surface-based techniques, which apply a surface detector to the sample array, then fit geometric primitives to the detected surfaces, and finally render the resulting geometric representation; (2) binary voxel techniques, which begin by thresholding the volume data to produce a three-dimensional binary array; the cuberille algorithm then renders this array by treating 1's as opaque cubes having six polygonal faces; and (3) volume-rendering techniques, a variant of the binary voxel techniques in which a color and a partial opacity are assigned to each voxel; images are formed from the resulting colored, semitransparent volume by blending together voxels projecting to the same pixel on the picture plane. Specialized display devices (stereo viewers, varifocal mirrors, cine sequences, real-time image-generation systems, and head-mounted displays) are described. Topics for future research are identified.