We introduce the Berlin Gehoerbildung Scale (BGS), a multidimensional assessment of music expertise in amateur musicians and music professionals. The BGS is informed by music theory and uses a variety of testing methods in the ear-training tradition, with items covering four different dimensions of music expertise: (1) intervals and scales, (2) dictation, (3) chords and cadences, and (4) complex listening. We validated the test in a sample of amateur musicians, aspiring professional musicians, and students attending a highly competitive music conservatory (n = 59). Using structural equation modeling, we compared two factor models: a unidimensional model postulating a single factor of music expertise; and a hierarchical model, according to which four first-order subscale factors load on a second-order factor of general music expertise. The hierarchical model showed better fit to the data than the unidimensional model, indicating that the four subscales capture reliable variance above and beyond the general factor of music expertise. There were reliable group differences on both the second-order general factor and the four subscales, with music students outperforming aspiring professionals and amateur musicians. We conclude that the BGS is an adequate measurement instrument for assessing individual differences in music expertise, especially at high levels of expertise.