Objective: This study addresses common errors that may occur during digital impression procedures using the CEREC AC and in-office CAD/CAM systems. Error types and frequencies resulting from digital impressions of the oral cavity were investigated and their origins identified to facilitate the acquisition of more accurate digital impressions. Method and Materials: A total of 1,251 digital impression cases, including 163 onlays and 1,088 inlays, were constructed as restorations using the CEREC AC system. Two evaluators determined five categories of digital errors as a basis for evaluation over two sessions. The five categories were as follows: inappropriate scanner positioning (ISP), improper handling of the scanner (IHS), irregular powder arrangement (IPA), improper cavity preparation (ICP), and insufficient scanned data (ISD). Results: The most frequently encountered errors were non-linear powder application (IPA), inappropriate oral cavity scanner placement (ISP), and insufficient data (ISD). ISP showed that inlays had a slightly higher frequency of errors, but this observation was not statistically significant (P > .05). Conclusion: Most errors are caused by incorrect operation of intraoral scanners or uneven application of powder in acquiring digital impressions. To provide optimal digital impression results, careful chairside technique procedures and operation of intraoral scanners are required. Keywords: common error, digital impression, in-office CAD/CAM, intraoral scanner