Since the disjunctive change of DSM-III, architects of the DSMs, including the recent DSM-5, have tended to ignore the problematic status of disorder categories limited by single symptoms or single symptom clusters. These disorders include kleptomania, pyromania, intermittent explosive disorder, paraphilic disorders, factitious disorder, among others. Single symptom/cluster disorders resemble Esquirol’s nineteenth-century French concept of monomania, which is defined as an “idée fixe, a single pathological preoccupation in an otherwise sound mind” (Goldstein 1998, p. 388). Monomania is also a variation on the early idea of partial insanity, where the patient’s reasoning remained unaffected, while insanity was circumscribed by either a single delusional belief or overwhelming irrational impulses. In this chapter I briefly review the history of monomania and why it came to be rejected by Anglo-European alienists. These historical critiques are then related to contemporary DSM-5 single symptom/cluster disorders. I then supplement this historical-to-contemporary critique with an original conceptual critique of single-symptom/cluster disorders. The chapter concludes with some methodological approaches to classification which address the crippling legacy of monomanias in today’s DSMs.