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When studying an extinct species such as the cave bear (Ursus spelaeus ROSENMuLLER 1794), it is possible to apply a variety of molecular biology techniques such as the study of stable isotopes or mitochondrial DNA (mDNA) to infer patterns of behaviour or physiology that would otherwise remain concealed. Throughout Europe and along time, differences in the isotopic values (delta C-13 and delta N-15) of cave bears arise from environmental differences and the Pleistocene climatic evolution. The climate determines the hibernation length, during which the cave bears undergo a particular physiology that can be related to an increase in delta N-15 during climate cooling. In order to verify whether hibernation affected the isotopic values, we compared cave bears in different ontogenetic stages. The results show that perinatal values reflect the values for mothers during hibernation, while juveniles show differences in maternal investment. A previous study in the literature based on complete mitochondrial DNA sequences of several individuals collected from closely situated caves showed that each cave housed, almost exclusively, a single lineage of haplotypes. This pattern suggests extreme fidelity to the birth site, or homing behaviour, and that cave bears formed stable maternal social groups, at least for the purpose of hibernation. Studies of this type offer unexpected data on the palaeobiology of this extinct animal.