To evaluate the impact off back injury on industry, the authors conducted a retrospective analysis of injuries among hourly employees of a large industrial manufacturer in western Washington. The Boeing Company provided injury information on 31,200 employees for a 15-month period from July 1, 1979 to September 30, 1980. Of the 4,645 injuries reported, 900 were back injuries. Claims related to back injuries constituted 19% of all workers' compensation claims but were responsible for 41% of the total injury costs, or approximately $1,800,000. The 90 most expensive back injury claims (10% of all back injury claims) were responsible for 79% of the total back injury costs. The percentage of back injury claimants with claims having a total incurred cost exceeding $10,000 (6.5%) was significantly higher than the corresponding percentage of claimants (1.5%) with claims for other than back injuries (P = 0.000). A similar significant difference was found concerning the tendency of back injury claimants to have multiple claims compared with the non-back injury claimants. This retrospective study reaffirms the significant economic impact of back injuries on industry, and specifically high-cost back injuries. In addition, it provides insight into factors associated with back injury and points to positive measures that may be taken to reduce back pain and economic loss. Characteristics of the back injury and employee-related factors associated with back injury are presented in two subsequent articles.