PUBLICATIONS FROM the Eye Disease Case-Control Study Group during the past 5 years1-6 have focused attention on the case-control design for clinical research in ophthalmology. However, case-control studies of eye and vision disorders did not originate with the Eye Disease Case-Control Study Group. Reports from case-control studies of varying size and quality have been published in the ophthalmologic and epidemiologic literature for more than 30 years.7-18 As noted by Seigel19 in an editorial published in the ARCHIVES almost 10 years ago, the case-control design is particularly suitable for research conducted within a clinical practice. Before embarking on a case-control study, the ophthalmologist should understand its principles and appropriate data analyses. This article describes design characteristics of case-control studies and calls attention to benefits as well as to potential pitfalls of this research design, particularly when conducted within the clinical setting.