The purpose of this investigation was to determine the best storage condition and time for pouring irreversible hydrocolloid impression material. Twenty-four irreversible hydrocolloid impressions were made of a maxillary plastic full arch dental model. Two storage conditions were used: storage in sealed bags and wrapping impressions with wet towels. Pouring of the impressions was carried out at 15 min, 30 min, 1 hr and 3 hrs after impression making. A Deltronic Profile Projector with x 15 times magnification together with a Computer Aided Analytical Geometry Program were used for measurement. The results of this study indicated that the magnitude of dimensional changes of irreversible hydrocolloid impressions stored in sealed bags and poured after 15 min ranged from zero to-228 µm, and that for those poured after 3 hour ranged from 22 to 272 µm. The dimensional change of casts made from impressions wrapped with wet towels and poured after 15 min ranged from 11 to 153 µm, while that for impressions poured after 3 hrs ranged from 92 to 145 µm. No statistically significant difference was found between the master model and casts from 15 min pouring time (P>0.05) . However, for 3 hrs pouring time and sealed bag storage condition, it was shown to be significantly different in respect to horizontal distances between left and right first molars (P=0.0017). If irreversible hydrocolloid impression pouring is to be delayed up to three hrs, then it should be wrapped with a wet towel and poured within 3 hrs, as this did not appear to affect their accuracy significantly. Irreversible hydrocolloid could be used as a final impression material for construction of Co.Cr. removable partial denture provided that the impression is poured within 15 min.