The accuracy of the present AE(12) index is evaluated by using magnetometer data from the six IMS meridian chains and other high-latitude stations. It is shown that the accuracy of AE(12) becomes progressively worse for lower values. There are at least a few causes for this inaccuracy, and three of them are identified. Although it is not possible to provide a single critical value, one should be cautious about the accuracy of the absolute value of AE (12) less than ~250 nT. In particular, since 70% of AE (12) values are less than 250 nT, one must be cautious in correlative use of the AE (12) index with solar wind parameters.