Recognizing the important role that compliance programs could play in helping health care providers & the enforcement community work together to reduce improper payments by Medicare, the author was asked to determine: (1) how prevalent are compliance programs among hospitals & other Medicare providers; (2) what costs are involved with compliance programs; & (3) to the extent effectiveness can be measured, how effective these programs are. This review focused almost exclusively on hospital & hospital-affiliated providers because they receive the largest share of Medicare funds & are the focus of several current enforcement actions. Tables.