Perimetry is a cornerstone in glaucoma management. The detection of glaucomatous visual field loss is of crucial importance for diagnosing the disease. Automated threshold perimetry makes thorough testing of the central visual field very possible and high-quality data are often achieved. Certain factors, however, may hamper the visual field examination or visual field interpretation. Many diseases other than glaucoma are known to influence the visual field in more or less predictable ways. Of interest is also low patient reliability, learning and fatigue effects, as well as test artifacts and suboptimal test strategies or parameters. Finally, statistical aids provided by the built-in computer of the perimeter must be judged keeping in mind the population from which the patient is derived. We describe such pitfalls in glaucoma perimetry, how they can be identified, and dealt with clinically.