Purpose: To evaluate the dimensional contour variations of acrylic resin denture bases before and after storage in water. Materials and Methods: The fit of 40 bases was evaluated by measuring the thickness of a layer made with silicone placed between the bases and the casts. The measurements were repeated on a new set of silicone layers after having stored the bases in water for 42 days. Results: Significant differences were found both for the maxillary and the mandibular bases. Conclusion: Water sorption had an important effect on the contour of the prosthetic bases.