The competing explanations for adverse health symptoms commonly observed in night-shift workers can be divided into “correlational” and “causational” groups. This study monitored health claims and costs over 3 years for all shifts in seven industrial plants and administered a survey canvassing a range of behavioral and attitudinal dimensions. Shift workers differed from day workers in symptomology and health claims, and, in their feelings of support from management, safety attitudes, and practices, felt support from friends and family, alcohol and tobacco use, and other dimensions. Because shiftwork was associated with adverse health effects but these other measured dimensions were not, the explanation that health effects are due to shiftwork itself rather than to its attitudinal or demographic correlates is supported.