This study verified the effect of the monomer/polymer proportion on the base adaptation of the complete upper dentures. Thirty stone cast-wax baseplate sets were packed in metallic flasks and the acrylic resin polymerized in water at 74 °C for nine hours. Three transverse cuts were made through each stone cast-resin base set, corresponding to regions: A) canines (anterior); B) first molars (median), and C) posterior palate (posterior). Measurements were made using an optical micrometer at five points for each cut to determine base adaptation: left and right marginal limits of the flanges, left and right ridge crests, and midline. Data were analyzed using to ANOVA and Tukey's test (5%). In region A there was significant difference among the monomer-polymer proportions, with a greater value of misfit for the content -25% monomer group and lower for the manufacturer's proportion group. In region B there was significant difference between the manufacturer's content (lowest value) and the monomer contents of +25% and -25% (both statistically similar). In region C there was significant difference among the monomer-polymer proportions, with greater value for the -25% monomer group than for the manufacturer's proportion. There was significant difference when the regions were compared in relation to the same monomer content. The best adaptation was in the region A and the worst in the region C. The amount of monomer exerted different effects on the adaptation of the denture base. In all regions, the smallest misfit was observed when the manufacturer's recommended proportion was used and the greatest misfit was observed in the -25% monomer.59341-7