Statement of the problem: Impression making is a critical clinical step to record accurately the three-dimensional intraoral relationships among implants, teeth and adjacent structures. Inaccuracy during impression making inevitably leads to laboratory errors resulting in lack of precision and misfit of the final prostheses. Several clinical variables may affect the precision of impression particularly in the presence of multiple angulated implants. Purpose: The aim of this study was to evaluate the effect of implant angulation and tray type on dimensional accuracy of open tray implant impressions. Materials and methods: A unilateral free end saddle dentate acrylic maxillary model resembling Kennedy class II starting from a missing canine was used in this study. Three models were duplicated from the acrylic model into epoxy resin master models. In each model, three implants were inserted in the sites of missing canine, second premolar and second molar. According to the direction of implant insertion, the master models were classified into three groups: Group 1: The three implants were inserted with 0° angulation (straight, control group). Group 2: The three implants were inserted with 15° angulation. Group 3: The three implants were inserted with 25° angulation. For all groups, open tray impressions were taken. Impressions of each group were subdivided according to the tray type into two subgroups: Subgroup A: Open tray impressions using custom made trays. Subgroup B: Open tray impressions using ready-made trays. All impressions were poured with type IV dental stone to obtain stone casts. Dimensional accuracy of the impressions was assessed using the travelling microscope. Reference distances were measured by standardized measurement protocol on the stone casts and compared with similar distances in the master models. Results: The results showed that there was a statistically significant difference between the three implant angulations. 25° angulation showed the highest mean of dimensional changes while, there was no statistically significant difference between 0° and 15° angulations in dimension II and III (P value = 0.009 & <0.001 respectively). Regarding the effect of tray type, the results showed that there was statistically significant difference in dimensional changes and the percent of dimensional changes between the two tray types in dimension III (P value = 0.019). Custom made tray showed statistically significant higher dimensional changes compared to ready-made tray. Conclusions: Impressions with ready-made trays showed less dimensional changes in case of 25° angulated implants.