Changes in the health care environment have impacted nursing workload, quality of care, and patient safety. Traditional nursing workload measures do not guarantee efficiency, nor do they adequately capture the complexity of nursing workload. Review of the literature indicates nurses perceive the quality of their work has diminished. Research has looked at tasks associated with nursing work, but not the nurse's perception of workload demands. Human factors research principles examine cognitive and perceptual abilities needed to meet the workload demands. A human factors framework focuses on mental demands and adds an understanding of why some demands are handled easily while others lead to mental overload and decreased performance. Study findings in human factors research indicate that human beings have the ability to attend to multiple details simultaneously and that the subjective perception of the worker is important in understanding the multiple, complex dimensions of workload. This review identifies the body of nursing workload research and establishes the need to include a subjective perception of the nurse as part of any workload measure.