INTRODUCTION: There are many contingencies, so many dentists do not pour their own impressions immediately which clears the need for extended-storage alginate impression materials. OBJECTIVES: Evaluating and comparing three extended-storage alginate impression materials concerning their dimensional stability. MATERIALS AND METHODS: One hundred and eighty (180) specimens were prepared in accordance with ADA specification No. 18 using three extended-storage alginates; Hydrogum5 (Zhermack), Cavex ColorChange (Cavex) and Blueprint X Crème (Dentsply). Following to ADA specification No. 19 dimensional stability was evaluated directly at six intervals; 0, 24, 48, 72, 96 and 120 hours using 10 specimens/interval /material. Specimens for delayed evaluation, were stored moistened within sealed plastic bags in a dark room at 23 ±1ºc. RESULTS: All impression materials showed initial expansion and ended with a net shrinkage. Cavex ColorChange showed the least dimensional changes. Dimensional changes of Cavex ColorChange, Hydrogum5 and Blueprint Xcrème ranged (0.14-0.59, 0.37-2.07 and 0.35-1.40% respectively). CONCLUSION: While Cavex ColorChange can be stored up to 120 hours without clinically significant dimensional changes, Hydrogum5 and Blueprint Xcrème should be poured immediately for the best results.