The Early Upper Palaeolithic of Europe is well-known for its remarkable symbolic expressions which demonstrate the capacity of early modern humans for abstract thinking, storytelling and communication by symbols and adornment. By contrast, the capacity for advanced technology and modern cultural behaviour in (late) Neanderthals is commonly perceived as limited despite recently accumulating evidence to the contrary. Here we report the discovery of a decorated bone item from recent excavations at Einhornhöhle in the Harz Mountains (northern Germany) that is engraved with a geometric motif composed of stacked-offset chevrons. The find is directly dated to ~51,000 years before present and the age is confirmed by further radiocarbon dates. These early dates assigns the decorated bone to late Neanderthals. Experimental studies suggest that the bone was pretreated before carving. The small excavation area produced cut-marked bones while diagnostic Middle Palaeolithic stone artefacts are present within a few meters distance inside the cave. For the first time, we successfully directly dated a decorated item of Middle Palaeolithic origin and our findings show that expressions of symbolic behaviour were part of Neanderthals’ behavioural repertoire before the early modern humans arrived in Central Europe. While located at the northern boundary of the Pleistocene human habitat, northern Central Europe has produced exceptional finds such as wooden weapons, bone tools, adhesives and now evidence for Neanderthal symbolic behaviour, suggesting that challenging environments may have prompted exceptional skills and cognitive abilities in Pleistocene pre-modern humans.