The prevalence of randomized controlled trials (RCTs) performed without fully informed prospective consent from subjects is unknown. We performed this study to estimate the prevalence of high-impact RCTs performed without informed consent from all subjects and examine whether such trials are becoming more prevalent. We performed a systematic review of English-language RCTs published from 2014 through 2018 identified in Scopus and sorted to identify the top 100 most highly cited RCTs each year. Text search of title and abstract included terms randomized controlled or clinical trial and spelling variants thereof, and excluded metaanalyses and systematic reviews. We independently identified the most highly cited RCTs based on predefined criteria and negotiated to agreement, then independently performed keyword searches, read, abstracted and coded information regarding informed consent from each paper and again negotiated to agreement. No quality indicators were assessed. We planned descriptive qualitative analysis and appropriate quantitative analysis to examine the prevalence and characteristics of trials enrolling subjects with other than fully informed prospective consent. We find that 44 (8.8%, binomial exact 95% CI 6.5% to 11.6%) of 500 high-impact RCTs did not secure informed consent from at least some subjects. The prevalence of such trials did not change over the 5 years (OR=1.09, z=0.78, p=0.44). A majority (66%) of the trials involved emergency situations, and 40 of 44 (90.9%) of the trials involved emergency interventions, pragmatic designs, were cluster randomized, or a combination of these factors. A qualitative analysis explores the methods of and justifications for waiving informed consent in our sample of RCTs.