Objectives: The purpose of this study was to evaluate the dimensional accuracy of stone dies produced from standardized impressions with 1 new and 1 conventional polyether impression material and a polyvinyl siloxane reference material. Methods and materials: Impressions with the polyether materials P2 and Impregum and with the polyvinyl siloxane Flexitime were produced at 23°C or 37°C from a truncated steel cone in cylindrical steel trays giving 4-mm impression layer thickness at the prominence line. Stone dies were poured after 1 or 24 hours of storage at ambient atmosphere. Additional impressions were stored at different relative humidity levels (0%, 33%, 50%, 75%, or 100%) for 24 hours prior to die pouring. The accuracy of the stone dies was determined as axial discrepancy between a steel ring, which fit perfectly on the steel die and the occlusal die surface. The base-diameter deviation (∆d) was calculated. Results: After 1 hour, a similar increase in ∆d was noticed for impression materials when dies were poured at impression temperature. Impressions made at 37°C exhibited significantly higher ∆d than at 23°C. Light-bodied P2 showed the highest ∆d increase when dies were poured after 24 hours. Flexitime showed moderate ∆d differences at the 2 pouring times. The ∆d of dies made from polyether materials decreased significantly with increasing humidity, whereas polyvinyl siloxane was not adversely affected. Conclusion: The dimensional accuracy of P2 is comparable to that of the conventional polyether impression material after short-term storage. Polyethers may absorb water, significantly compromising die accuracy upon storage at high humidity. Keywords: dimensional accuracy, elastomeric impression materials, polyether, polyvinyl siloxane, storage humidity, storage time