"Are you ready?" Amy Hopkins asks a visitor as the two stand outside her one-bedroom apartment in Ballston.

She's a self-described hoarder. And it's true, she does have a shelf of cookbooks even though she doesn't cook much, has an overstuffed bedroom closet and a living room cluttered with junk mail and magazines. But she's nowhere near the most serious example of what can be a debilitating, humiliating obsessive-compulsive disorder.

"Most hoarders are extremely ashamed and embarrassed by their situation," says Prof. Fugen Neziroglu, co-author of "Overcoming Compulsive Hoarding."

The condition can be extreme. Such as the man forced to eat out every day because he can't open his refrigerator door -- piles of magazines are blocking it. Or the woman whose car is stuffed to the ceiling with food wrappers and soda cans, with only a small area hollowed out for the driver. Or the woman in Falls Church who was charged with petty larceny last summer after digging through her neighbor's trash and hauling her finds back home. She had been sleeping in her back yard because every room in her house was crammed with refuse.

Compulsive hoarding, as defined by Neziroglu and her co-writers, Jerome Bubrick and Jose A. Yaryura-Tobias, is "acquiring and saving items that have little or no value and then having tremendous difficulty discarding them."

Neziroglu, a behavior psychologist who teaches at New York University and Hofstra University, says there's no prevalent data on the number of hoarders in the United States. The estimate widely used is about 1 percent of the population.

"But my guess is that it's a lot more," she says. "It seems like everyone I speak to knows someone who's a true hoarder."

Hoarding can occur at any age and cuts across class lines, according to the authors.

So what about the co-worker who never throws away old files, or has books and magazines piled a mile high?

The teenager whose room is always a pigsty?

Your own seeming obsession with keeping absolutely every receipt, even for the most minor purchase?

And just what is the difference between a hoarder and a collector?

According to Neziroglu's book, collectors are proud of what they have acquired, often have a space where the items are displayed and will budget financially to acquire their items, be they stamps or baseball cards.

Hoarding is another matter. According to the authors, you should worry that you are a hoarder when you begin to feel distressed about your possessions -- ashamed of what you've accumulated; when you find yourself losing functional space -- whether it's at home or at the office; and when you and others have trouble simply moving around the space. The ultimate sign, however, is the feeling that you can't correct the situation.

Fear is a part of the hoarding life. A hoarder may be afraid of losing information, of making a mistake by throwing something out. Depression and anxiety are also often factors. In its worst forms, the disorder can drastically disrupt lives, ruining finances and families.

Hoarding has gotten more attention in the last five years or so, says Neziroglu, and some local governments are learning to respond more sensitively to the extreme cases.

Amy Hopkins's apartment has a bit of a thrift store scent. The hall leads to a living room cluttered with junk mail, magazines and knickknacks.

She can open the bedroom door only halfway. A pile of shoes, gift boxes and unopened merchandise is blocking the space between the door and the packed closet. Suits and dresses are also hanging in her bathroom: on the towel hooks, the shower rod, the bathroom door.

"I moved here a year ago," says Hopkins, 61, who left her home in Arizona to be closer to her daughter and two granddaughters. "You should have seen my old house. This isn't nearly as bad."

Although Hopkins's situation isn't a severe case (some extreme hoarders keep separate houses for what they've accumulated), it's apparently bad enough. She was recently notified by the apartment building's management that she has until Friday afternoon to clean up the place. "If someone wanted to come in and help me clean, yes, I think that would be fine," says Hopkins.

"I think it's an extreme form of sentimentality," says Hopkins's daughter, Yvette Hopkins. "Every object has a moment attached to it, and that's hard to let go."

Neziroglu says sentimentality is certainly one of the motivations to hoard.

Treating the disorder requires a gradual approach, she says. When she counseled her patients, "the most important thing was that I had to carry the discarded items away with me," or else the person would go through the bags again, she says. Most hoarders are very private people who won't allow someone to help them. "But, yes, it's much preferable for someone to be there with them -- at least someone to take the trash away."

Yvette Hopkins says she and her daughter Lillian, 9, have also been known to hold on to too many things. Her husband helps reduce the accumulation, she says, although he has a harder time with their daughter. Her husband recently removed several bags of junk from Lillian's room when she was away at summer camp, knowing that she would never cooperate otherwise.

"One time Lillian went to the back yard and looked through the trash cans to find her stuff," says Yvette. "She came back and had made my husband a gift for his birthday -- it was this little ornament that she had made from the trash he had thrown out. She said, 'See, Daddy? What you throw away is my treasure.' It was quite sweet."

Not in Neziroglu's book.