Dendritic spines are key structures for neural communication, learning and memory. Spine size and shape probably reflect learning and synaptic strength. With superresolution STED microscopy (STimulated Emission Depletion microscopy) we imaged for the first time in 3D the detailed shape of the majority of the spines of individual neurons in turtle cortex (Trachemys scripta elegans) (Figure, scale bars: upper row 0.5 µm, lower row 1 µm). A combination of skeletonization in 3D and segmentation of almost 7000 spines allowed us to describe their morphology in detail. To classify the spines, we clustered them according to their shapes and lengths. The clustering revealed several distinguishable shape classes (“Stocky”, “Dwarf”, “Club-like”, “Balanced“, and “Delicate” spines). Importantly, dendritic spines of a given class were not distributed randomly, but rather decorated significantly more often some dendrites than others, i.e. each dendrite had a unique signature, made of different ratios of each spine class. In addition and independently of the clustering, we described the spines with several morphological parameters. The individuality of dendrites was corroborated by significant inter-dendrite differences in these parameters such as head size, length and spine density. In addition, we found many spines that were branched or were decorated with spinules of various forms. These findings may have implications for the computational role of individual dendrites.