AIM: To provide age- and gender-specific reference values for orbital fat and muscle volumes in Caucasian adults. METHODS: Computed Tomographic (CT)-scans of 160 orbits from 52 men and 55 women, aged 20 to 80 years, not affected by orbital disease were evaluated. Orbital bony cavity volume (OV), fat volume (FV) and muscle volume (MV) were calculated by a previously validated method using the software program Mimics(R).Ratios of fat volume to orbital bony volume (FV/OV) and of muscle volume to orbital bony volume (MV/OV) were determined. RESULTS: OV, FV and MV were all significantly larger in men than in women (p<0.001), but FV/OV and MV/OV were similar in both sexes. OV and MV did not change with age, but FV increased with advancing age in both women (p<0.001) and men (p<0.001). Linear regression analysis with FV/OV and MV/OV ratios as dependent variables and age and gender as independent variables showed a significant correlation between age and FV/OV (r=0.52, p<0.0001) and age and MV/OV (r=-0.26, p=0.001). CONCLUSIONS: Advancing age is associated with an increase of FV/OV and a minor decrease of MV/OV. Gender-specific differences in orbital FV and MV disappear once FV and MV are related to the orbital bony cavity volume (OV), by calculating the ratios FV/OV and MV/OV. Age-specific gender-neutral reference ranges (2.5 and 97.5 percentiles) of FV/OV and MV/OV are presented.