Introduction. Alginate masses, due to their numerous advantages, are often used as an impression material in prosthetic treatment. Storage conditions of alginate impressions are crucial for stability of its dimensions. The development of technologies used in modern dental prosthetics determines search for the highest possible accuracy and predictability in representation of prosthetic field. In everyday practice, prosthetic laboratories are rarely a part of dental offices, what makes reasonable to determine the optimal conditions for storing impressions made with alginate masses. Aim of the study. To determine the influence of storage conditions of alginate mass impressions on their spatial dimensions. Materials and Methods. Forty cubic alginate samples were made and divided into 8 groups. Each group of samples was stored in a diverse environment of temperature and humidity. Storage conditions were controlled by digital hytherographs. The spatial dimensions of samples were measured using an electronic vernier caliper with an accuracy of ± 0.02 mm, immediately after setting time of alginate mass and after 24 and 144 hours of storage. The results of the measurements were analyzed using descriptive statistics as well as Kruskall-Wallis test. Results. The smallest change of the dimensions of tested samples was observed in the group stored in humidity of 65% and at a temperature of 7.5° C (after 24 hours) and 24.4° C (after 144 hours). The largest dimensional change was noted in groups stored without increased humidity values and in the alcohol-based solution of the disinfecting liquid. Conlusions. 1. Increased humidity ensures the smallest change of the dimensions of impressions taken using alginate mass. 2. Lowering the storage temperature positively influences the dimensions of the tested samples. 3. Alcohol-based disinfectants should not be used for storing alginate impressions because they reduce the size of the tested samples.