Background: The accuracy of full-arch digital implant impressions has not been investigated yet and clinically relevant data are nonexistent. Aim/Hypothesis: Purpose of this study is to compare the accuracy of digital and conventional impressions for completely edentulous patients and to determine the effect of different variables on the accuracy outcomes. Null hypothesis was that there would be no difference between full-arch digital and conventional impressions. Material and methods: A stone cast of an edentulous mandible with five implants was fabricated to serve as master cast (control). The master cast was scanned and digitized with an intraoral scanner (TRIOS; three shape). Ten digital impressions were taken with the same intraoral scanner after connecting plastic scanbodies and digital models were created (n = 10). Four different conventional impression techniques were used to fabricate four groups of casts (n = 10). The implant casts of these four groups were also digitized with the same intraoral scanner into digital models. The scanning datasets from the five groups of digital and conventional impressions were superimposed with the one from the master cast to assess the 3-D (global) deviations. The 'best fit' algorithm was used with computer software to superimpose the scanning datasets and assess the accuracy of each impression technique. Results: Paired t-test was used to compare the 3-D discrepancies between the five test groups and the master cast, respectively. Significant difference was found at the 3-D accuracy between group II (non-splinted implant level) and control (P < 0.05). No statistically significant differences were found between the other test groups I, II, IV and V and the control (P > 0.05). Conclusion and clinical implications: The full-arch digital implant impressions were as accurate as conventional implant impressions and the null hypothesis was corroborated. The splinted implant-level impressions were more accurate than non-splinted implant-level for completely edentulous patients and as accurate as the digital ones.