There is substantial disagreement regarding the impact of hospitalists on costs, quality, and satisfaction with inpatient care. The authors reviewed 21 evaluations of the use of hospitalists in U.S. hospitals. Most evaluations found that patients managed by hospitalists had lower total costs or charges than patients in comparison groups and that these savings were achieved primarily by reducing length of stay. Most evaluations found no statistically significant differences in quality of care or satisfaction. However, lack of random assignment limits the ability to draw causal inferences from many of the evaluations. All randomized studies were conducted in teaching hospitals, raising questions as to the generalizability of findings to nonteaching hospitals. Further research is needed to better identify the mechanisms by which hospitalists reduce length of stay and to ascertain which types of hospitalist programs are most effective and which patients are most likely to benefit.