This paper reviews the role of empathy in autism spectrum disorders and psychopathy. Empathy can be subdivided into two categories: cognitive empathy (i.e., the ability to identify the emotions of others) and affective empathy (i.e., the ability to share or match the emotions of the self with those of others). Individuals with autism spectrum disorders lack cognitive empathy, whereas individuals with psychopathy lack emotional empathy. The similarity hypothesis states that people empathize with other people who are similar to themselves in personality and in conditions such as developmental disorders or typical development. The similarity hypothesis predicts that individuals with autism spectrum disorders would emotionally empathize with other people with autism spectrum disorders, and individuals with psychopathy would cognitively empathize with other people with psychopathy. Finally, we attempted to interpret autism spectrum disorders and psychopathy as resulting from the neurodiversity of empathy.