El Castillo cave is a well-known site because of its Paleolithic archaeology and parietal rock art. is paper is focused on the human remains found by V. Cabrera in the Mousterian Unit XX assigned to MIS 4 and early MIS 3. e fossils consist of one upper left second premolar (ULP4), one incomplete proximal hand phalanx, and one partial femoral head. e tooth and the phalanx were assigned to adults, whereas the femoral head belonged to an immature individual due to the absence of fusion traces to the metaphyseal surface. e external morphology and metrical characterization of the Castillo-1466 (ULP4) tooth crown was quanti ed and compared to the variability of other Neanderthal dental remains and a sample of modern human populations. We also quanti ed its 3D enamel thickness distribution, its roots morphology, as well as the presence of chipping, and their possible relation to masticatory or paramasticatory activities. Castillo-1466 shows crown dimensions compatible with middle-sized Neanderthal teeth, but with a remarkably thicker enamel than other Neanderthal premolars, such as Marillac 13. e femoral head and the hand phalanx fragment are compared to published values for Neanderthals, although both partial fossils lack diagnostic features precluding any clear taxonomic diagnostic. erefore, their attribution to Neanderthals is assumed based on the dating of the layers in which they were discovered. El Castillo cave Mousterian fossils represent another contribution to the knowledge of the Middle Paleolithic populations of Northern Spain, where di erent sites along the Cantabrian mountains yielded several human remains assigned to MIS 4 and early MIS 3.