This paper outlines a diagnostic entity called 'Pathological Habit Disorder' which is suggested for inclusion in the DSM as an Axis II option. Specific areas of concern, either mental (Axis I) or physical (Axis III), would delineate the syndrome. Pathological Habit Disorder (PHD) points to treatment options where the syndrome is wholly or partly habit-driven. Whether the syndrome is habit-driven or not will remain a clinical judgement even though many conditions, previously thought immutable except by medication, are proving accessible to behavioural engineering. In the ICD system, PHD seems to fit in "Special Symptoms or Syndromes not elsewhere Classified". It is demonstrably useful to have a diagnosis such as PHD and to incorporate it into the body of medical classification, recognizing current practices for dealing with unwelcome or damaging habits.