One of the themes in this story is the idea of madness and how it affects human nature and humanity. Poprishchin, the main character, begins his descent into madness and seemingly begins to lose his humanity in the process. As he grows more insane, he is unable to maintain his relationships with others, and he becomes wrapped up in himself internally. Interestingly, he writes about the correspondence between the dogs he believes he has found. This shows that mentally, he is no longer relating with humans so much—and that perhaps another species seems more similar to his own mental state and ability.

Another theme in the work is the idea of self-aggrandizement. Often with paranoid schizophrenia, narcissistic personality disorder, or several other severe mental disorders, people begin to see themselves as vastly more important than they truly are. In the case of this story, Poprishchin believes that he is the rightful heir to the throne of Spain and takes steps to let people know this, such as by making a handmade Spanish royal uniform and wearing it out and about.

A final theme in the work is the idea of alienation. Through his mental illness, Poprishchin is slowly but steadily separated from those around him. He isolates himself from company, retreats from work, and becomes more internalized. Unfortunately, this is all too common and tends to make the mental illness much more severe, because the individual is left to spiral in their own thoughts instead of working through them with an outside observer who can help them see the folly in their reasoning.