There is uncertainty about actual gear accuracy due to improper acceptance codes of gears. In this paper the magnitude of the influence of this uncertainty on the state of tooth fillet stress, contact stress of tooth flanks, flash temperature on tooth flank and exciting force of machine vibration caused by gear meshing are discussed. It is pointed out that there were some cases in which the deviation of the tooth flank form from the intended one, by which the maximum values of contact stress, flash temperature and gear vibrational excitation were strongly affected, could not be found by the normal gear accuracy checking procedure defined in current standard specifications. It was shown that the influence of the deviation of the tooth flank form was so large, that the reliability of the gears could not be guaranteed, and that the machine vibration or gear noise of the machine become far removed from the intended level or specification limit. Gear accuracy also changes the amount of gear alignment error, which affects the power transmitting characteristics of gears.