This paper describes an experimental and epidemiological investigation of the potential application of a specific rollover occupant protection system, consisting of a rollover protective structure and occupant restraint (collectively referred to hereafter as ROPS), to all-terrain vehicles (ATVs). The ROPS investigated in this paper was proposed by Dahle  as a means to improve the safety of ATV operation. Crash tests were performed with an unhelmeted instrumented dummy on 4-wheel ATVs equipped with the prototype Dahle ROPS (hereafter referred to as D-ROPS); the test results established that the D-ROPS design exhibited the potential for serious injury or death in lateral rollover, rearward pitchover, collision, and oblique frontal impact accident scenarios. Review of ATV-associated 1986 fatality reports from the U.S. Consumer Product Safety Commission (CPSC) indicated that, in a majority of cases, it would have been unlikely that adding D-ROPS to the ATVs would have prevented serious injury. Examination of ATV-associated injury reports from the CPSC's 1985 ATV Injury Survey suggested that many accidents that resulted in only minor injuries without a D-ROPS probably would have produced more serious outcomes if the vehicles had been equipped with D-ROPS. Consistent with our other studies, which indicate that ROPS limit ATV rider activity and adversely affect vehicle performance characteristics, handling, mobility, and utility, the results of this investigation indicate that ROPS in general, and the D-ROPS in particular, are inappropriate for ATVs.