In-vitro study was carried-out to compare the dimensional accuracy of three different viscosities of additional elastomeric poly vinyl siloxane impression material (PVS). An ideal model of maxillary partial edentulous case (Kennedy Class II modification 1) was selected as master models. Then standard references marks were placed in the acrylic cast by using a metallic pins and before the fabrication of the custom tray a five box shaped indices were prepared in the model. Then a transparent heat cure acrylic resin tray was fabricated on the acrylic cast to make the impressions, the tray fit into the box shaped indentations on the cast so it will return to the same position each time.Four groups for the impression material were classified according to the viscosity used to the following:•Group 1: ten impressions were made for the acrylic model using light body viscosity.•Group 2: ten impressions were made for the acrylic model using medium body viscosity.•Group 3: ten impressions were made for the acrylic model using heavy body viscosity.•Group 4: ten impressions were made for the acrylic model using the above three viscosity in single tray.Measurements were carried out for the length, width and the cross of the master model and comparing them with the stone casts. Then, the measurements were made for the all casts groups by two methods:•First method:By using the digital caliper which capable of measuring up to 0.01 mm•Second method:By using digital camera all casts were photographed and the casts images were imported into computer where they subjected to special measuring software program. then using special software program convert cast images to three dimension image, then dimensional difference measurements were made by full field 3Dcomparison of obtained casts (image subtraction technique).From this study it was concluded that:1.The results show that there was no statistically significant difference between the measurements made by computerized and Digital caliper methods.2.The poured casts obtained from medium viscosity polyvinylesiloxane impression material were more dimensionally accurate than those produced by light body PVS, heavy body PVS and from the three viscosities together.