The American Cancer Society says three-quarters of long-term smokers will have serious health problems; smoking will kill half of them.

It's the primary cause of lung cancer, which kills 160,000 Americans a year — the equivalent of one jumbo jet crashing every single day.

Seventy percent of smokers say they want to quit, and 35 percent of them say they try.

"I know in my heart, in the not too distant future, getting close to the point where I actually will just one day stop smoking," said smoker Sandy Masone.

But less than 5 percent actually succeed in kicking the habit.

Nicotine is a fast-acting drug, reaching the brain seven seconds after it's inhaled — faster than marijuana, cocaine or heroin.

But cigarettes contain more than just nicotine. Some 4,000 chemicals — including 60 known carcinogens — are released by every burning cigarette. The chemicals include substances also found in arsenic, nail polish remover, rat poison and the insecticide DDT.

"I don't think there is anybody out there that is unaware of what it's doing to them," said Jose Rich, who smokes.

Yet one-quarter of high school students are hooked before graduation.

Fifteen-year-old Nicole said she smoked because, "It's a good conversation starter: 'Hi, do you have a cigarette?'"

Generations of Americans Sold on Smoking

Madison Avenue has sold smoking to generations of Americans — from Lucy and Ricky to today's advertisements, which marry smoking and "the good life" in magazines, on Web sites, and even race cars.

A record $15.4 billion was spent on marketing cigarettes in 2003, dwarfing the anti-smoking campaigns, which spend one-one thousandth of that amount.

For many smokers, tobacco road often ends at the doctor's office. A surgeon general's report last year linked smoking to cancers of the cervix, kidney, pancreas and stomach.

Mickey McCabe smoked for 30 years, and had lung cancer to prove it. She survived the disease, but barely — doctors removed the middle lobe of her right lung.

"Anything I can do to promote somebody not going down that road, I would do it," she said.

This week, cigarette maker Philip Morris will celebrate the 50th birthday of Marlboro. It's the most popular brand of cigarettes in America by far, and sales are booming.

ABC News' Dean Reynolds filed this report for "World News Tonight."