Although safety belt use increases after passage of a safety belt law, the statewide direct and indirect cost savings associated with increased safety belt use after a belt use law has been enacted is not known. We analyzed a subset of data from the Iowa Safety Restraint Assessment consisting of 997 injured motor vehicle occupants treated at any of 11 Iowa hospitals from throughout the state between November 1987 and March 1988. We found that injuries were more serious and that more deaths and cases of permanent disability occurred among persons who did not wear safety belts. Failure to use safety belts was independently associated with higher payments to hospitals by health care insurers and individuals in nearly all age, sex, and vehicle speed categories. Lifetime direct and indirect cost savings associated with Iowa's safety belt law for persons injured in one year were estimated to be $69.5 million.