In this chapter we will examine the substantial overlap, similarities, and also connections between people with Hoarding Disorder, Obsessive Compulsive Personality, Attention Deficit Hyperactivity Disorder, and Autism. The importance of ADHD in many people with hoarding will be examined along with a discussion about how the increasing recognition of a link between the two conditions has led to research into new ways of treating Hoarding Disorder. It is also recognised that autism interacts with hoarding as well as ADHD in a number of ways. Some people with autism are unable to tolerate any clutter at all whilst others hoard huge numbers of items due difficulty in decision-making. In addition, a substantial proportion of people with autism also have a diagnosis of OCD. As has already been discussed (Chapter 5), OCD may present with hoarding symptoms due to the nature of obsessive thoughts as well as Hoarding Disorder also.