Hierarchy similarity measure techniques are described. In one or more implementations, categories in a hierarchy of categories are assigned to each of at least two objects. A similarity score may be calculated for the at least two objects that takes into account the categories assigned to the objects. To compute the similarity score for the objects, a distance in the hierarchy between the categories assigned to the objects may be used. Further, a number of siblings in the hierarchy of the categories assigned to the at least two objects may be used to compute the similarity score for the objects.