Use of optical 3D digitization for dimensional and shape inspection of work-pieces has increased during the last few years. However, the quality of data obtained by scanning may be affected by many factors. Digitization accuracy of optical 3D scanners is generally determined by Acceptance Tests compliant with the VDI / VDE 2634 standard. When performing the validation test, all variables and measurement conditions must basically be ideal. Unfortunately, such conditions are usually unavailable in common practice. For that reason, we conducted research finding how may the surrounding conditions and parameters of digitization process affect the dimensional and shape accuracy of optical 3D measurement. The aspects we assessed were for example calibration, exposure, number of images, scanning angle, or quality of used reference points. The measurement was carried out on ATOS optical 3D scanner by GOM and spherical and cylindrical elements were used for the analysis. As found out, used reference points with low quality have a major impact on quality and accuracy of the result. Operators should also pay increased attention to calibration and heat-up the scanner to operating temperature before commencing the measurement.