Long-term follow-up was recorded on the visual fields of 251 patients with chronic open-angle glaucoma and 826 patients with ocular hypertension. Observation periods exceeded ten years for 73 patients with manifest glaucoma. Initial glaucomatous defects appeared in 98 eyes of 72 patients while under continuous observation. Initial defects were characteristically shallow and were located most commonly in the superior Bjerrum region adjacent to the blind spot. Three-dimensional (contiguous area) static perimetry provided superior resolution in detecting and characterizing the full extent of such shallow defects. The chronologic course of initial defects defects was marked in 22 of the 98 eyes by a phenomenon of a transiently appearing defect. Disappearance and reappearance of transient defects did not occur synchronously with short-term fluctuations in intraocular pressure. Ten-year follow-up of 63 eyes with manifest glaucomatous defects showed a high incidence (73%) of progression to dense involvement of the originally affected altitudinal hemifield. All eyes were treated continuously, but visual field loss occurred in spite of only marginally elevated levels of intraocular pressure.