Background. In a recent out-of-hospital cardiac arrest (OHCA) trial conducted under an initial waiver of informed consent (IC) (21 § CFR 50.24), data from public records were collected that shed light on whether the willingness to provide subsequent IC was associated with study outcomes. We hypothesized that IC was less likely to be obtained in subjects with significantly compromised health status. Methods. A post hoc analysis was conducted using data from a National Institutes of Health–funded randomized, controlled OHCA clinical trial comparing active compression–decompression cardiopulmonary resuscitation (CPR) plus an impedance threshold device (ACD+ITD) with standard CPR. The primary end point was survival to hospital discharge (HD) with favorable neurologic function [Modified Rankin Scale score (MRS) ¡Â3]. The status of the consent process was tabulated for all subjects who survived to hospital admission. Unadjusted Fisher’s exact test and associated odds ratios were used to compare the MRS at HD by IC status. Results. Among a total study population of 1,655 subjects, 457 survivors were admitted to the hospital, and 440 had known HD status: 320 gave IC, 46 were unable to complete the IC process (the instititional review board allowed medical record review), and 74 denied IC. Survival with an MRS ¡Â3 was significantly higher in subjects where IC was given: 35.0% vs. 4.1%, p < 0.001. Sixteen of the 17 cases with missing MRS outcomes were in the IC-denial group. Even if all were considered to have favorable outcomes, the resulting rate (21.1%) was less than that seen among the subjects with IC given (p = 0.015). Conclusion. The subjects who denied IC were significantly less likely to have favorable outcomes. These findings suggest that some resuscitation trials may unknowingly underrepresent those subjects with the worst prognoses in a target study population despite prespecified inclusion and exclusion criteria, because of the unwillingness or inability of the subjects or their families to provide IC.