This study investigates shear-wave propagation across the Hellenic subduction zone using high-quality waveforms of 71 intermediate-depth events (40-160-km depth). The data have been recorded by a permanent seismic network consisting of 22 broadband, three-component stations that cover most parts of Greece. Shear waves can be efficiently transmitted with low attenuation (Qs ∼ 1100) through the descending slab, which extends laterally over much of the forearc area with a northwest-southeast strike. The slab also appears to be continuous downdip in the depth range 60-160 km, even though it was found that a gap smaller than 10 km would not affect shear-wave efficiency significantly. Two highly attenuating areas have been detected, one in the central/southeast Aegean corresponding to the mantle wedge and the other in the northern Aegean, probably caused by elevated upper mantle temperatures owing to the ongoing extension in that area. These results provide additional constraints for the geometry of the Hellenic subduction zone and the geodynamic setting of the Aegean region.