Frost and Hartl (1996) provided the first systematic definition, identifying three characteristics:"(1) the acquisition of, and failure to discard a large number of possessions that appear to be useless or of limited value; (2) living spaces sufficiently cluttered so as to preclude activities for which those spaces were designed; and (3) significant distress or impairment in functioning caused by the hoarding." This definition distinguished hoarding from the collecting of objects generally considered interesting and valuable.
Go to this site for further definitions 

Dr. David Tolin says you may have a compulsive hoarding problem if you meet all three of these criteria.  http://www.oprah.com/article/oprahshow/home_hoarding_resources

1. You regularly hang onto a large number of possessions that most other people would not consider to be  very useful or valuable.
    For example, many people with compulsive hoarding problems hang onto things like:
 

·         Junk mail

·         Old catalogues and newspapers

·         Things that might be useful for making crafts (although you don't 

      actually get around to using them for that purpose)

·         Things that you think you might want to give to others as gifts 
(although you never actually give them)

·         Clothes that you think you might want to wear someday 
(but you don't actually wear them)

·         Broken things that you think you might want to fix someday (but you 

      never actually get around to fixing them)

·         "Freebies" that you pick up

2. Your home, or parts of your home, is so cluttered that you can no longer use those parts of your home for their intended purpose.
    For example, many people with compulsive hoarding problems have:

·         Beds that they cannot sleep in

·         Kitchens that they cannot cook in

·         Tables that they cannot use for dining

·         Chairs or sofas that they cannot sit on

3. The clutter is bad enough that it causes significant distress or impairment. For example, many people with
    compulsive hoarding problems report that they:

·         Cannot have friends or family over to their homes because they are so embarrassed by the clutter

·         Cannot let repair or maintenance professionals into their homes because they don't want them to 
see the clutter, so things don't get fixed

·         Keep the shades drawn so that no one can see inside

·         Get into a lot of arguments with family members about the clutter

·         Are at risk of fire, falling, infestation or eviction

·         Feel depressed or anxious much of the time because of the clutter

If you recognize yourself in these compulsive hoarding signs, Dr. Tolin explains how some treatments may
help people to manage the symptoms.
http://www.oprah.com/article/home/homeimprovement/tows_past_20041118_b/1
http://www.oprah.com/article/home/homeimprovement/tows_past_20041118_b/3

Some of this information was adapted by:  Dr. David Tolin from Steketee & Frost (2003), Clinical Psychology Review, 23, 905-927

More Information:
You can find resources on compulsive hoarding and its treatment at these websites:

·         Free materials from Dr. Tolin on complusive hoarding: http://www.instituteofliving.org
/ADC/compulsive_hoarding.htm

·         Obsessive Compulsive Foundation: http://www.ocfoundation.org/hoarding/