Abstract This article analyses the political and scientific controversy surrounding a race science project undertaken by the anthropologist Egon Freiherr von Eickstedt under National Socialism. Beginning in 1934, Eickstedt and his team of assistants conducted a series of racial studies on the population of Upper Silesia, a contested borderland in East Prussia. Motivated by a nationalist desire to counter the work of Polish anthropologists in the region, Eickstedt argued that the population of Upper Silesia belonged predominantly to the so-called ‘Nordic race’ and that the territory was thus fundamentally German. Nazi officials, however, viewed the Silesian studies with alarm, since the results also appeared to show that people in the area were a racial mixture and that the ‘Nordic race’ made up less than 40 per cent of the population in some locales. They worried that Eickstedt’s studies could undermine Germany’s territorial claims in the region and threaten national unity. The ensuing controversy presents a case in which the anthropological concept of ‘race’, rather than serving its usual role in Nazi thinking as the biological underpinning of the Volk (or people), threatened to undermine its coherence. The reaction to Eickstedt’s Silesian studies demonstrates a lack of consensus on race within the Nazi system, suggesting that understandings of race in Nazi Germany were neither as coherent nor as uniform as the paradigm of the ‘racial state’ has assumed.