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This study aims to evaluate the indices of glandular dose heterogeneity in full-field digital mammography. The distributions of GD in a breast phantom with a skin layer of 4 mm were determined using the Monte Carlo method with simulated x-ray fluence spectra. First, the GD to air kerma (GD/ K air ) volume histogram was obtained from the GD distributions, which were indicated by the glandular volume (%) as a function of GD/ K air . The GD indices, namely, the maximum glandular dose (GD 2% ) and glandular volume percentage (%) receiving at least the mean glandular dose (MGD) ( V MGD ) were calculated from the GD/ K air volume histogram. Next, the scatter plots of GD 2% /MGD and V MGD /MGD were more affected by breast thickness than glandularity and tube voltage, and they decreased according to the power law of DgN for all the target/filter combinations. The values of 2% were proportional to DgN and decreased with increase in the compressed breast thickness. The values of (MGD) i and ( V MGD ) i were obtained from the relationship between the GD indices and DgN for 596 clinical irradiation cases based on individual irradiation conditions. The values of GD 2% /MGD were more affected by breast thickness than glandularity and tube voltage, and they decreased according to the power law of DgN for all the target/filter combinations. The values of V MGD were proportional to DgN and decreased with increase in the compressed breast thickness. The values of (MGD) i and (GD 2% are mainly affected by breast thickness. These indices are useful for the evaluation of glandular dose heterogeneity in mammography. i for 596 clinical irradiation cases were estimated to range from 0.6-3.0 mGy to 1.1-7.0 mGy, respectively, and ( V MGD ) i was in the range 32%-48%. (GD 2% ) i and ( V MGD ) i are mainly affected by breast thickness. These indices are useful for the evaluation of glandular dose heterogeneity in mammography., (© 2020 Society for Radiological Protection. Published on behalf of SRP by IOP Publishing Limited. All rights reserved.)