We conducted a randomized, double-blind, phase III yellow lever (YF) vaccine trial among 1,107 healthy children in Sullana in northern Peru. The safety and efficacy (by measurement of geometric mean neutralizing antibody titer responses) were determined for two YF vaccines. ARILVAX™ (n = 738) and YF-VAX® (n = 369). Seroconversion rates were higher (94.9%) in ARILVAX™ than in YF-VAX® (90.6%) recipients. The two-sided 95% confidence interval (YF-VAX®-ARILVAX™) was (-12.8% to -2.5%). indicating that the higher seroconversion rate for Arilvax™ was significant. Post-vaccination (30-day) mean log10 neutralization indices were found to be similar for both products: 1.32 for ARILVAX™ and 1.26 for YF-VAX® (P = 0.1404. by analysis of variance). A similar number of subjects in each group reported at least one adverse event (AE): 441 (59.8%) for ARILVAX™ versus 211 (59.9%) for YF-VAX®. Most (591: 96.7%) of these were of a mild nature and resolved without treatment. There were no treatment-related serious AEs. This is the first randomized, double-blind comparison of two YF vaccines in a pediatric population: both vaccines were shown to be highly immunogenic and well-tolerated. Copyright © 2005 by The American Society of Tropical Medicine and Hygiene.