Few well-controlled studies have assessed the extent and magnitude of adverse health conditions reported by video display terminal (VDT) operators. To evaluate the association between typical, daily VDT use and the prevalence of adverse conditions related to vision, musculoskeletal conditions, headaches, and colds or sore throats, we conducted a cross-sectional, epidemiologic study of 1,545 Massachusetts clerical workers. The study results indicated an increased prevalence of adverse conditions pertaining to vision, musculoskeletal discomfort, and headaches among clerical workers who used VDTs. The magnitude of the increased prevalence was dose dependent. The effects related to musculoskeletal discomfort and headaches were higher among VDT workers in computer and data processing services, public utilities, and the Commonwealth of Massachusetts than among workers in banking, communications, and hospitals. These latter effects, however, may have been due to random variation.