Even a year after Sept. 11, Chicago resident Kevin Richardson still won't get on an airplane.

"I have not flown anywhere since then," the 31-year-old computer consultant said. "Usually I fly at least once or twice a year, but this year I have not gone anywhere. I am afraid of flying, or actually I'm afraid that once I start flying I'll develop a fear of flying."

Richardson's post-Sept. 11 anxiety even forced him to cancel a short air trip from Chicago to Detroit to attend a friend's baby's birthday. And Richardson's address on the 54th floor of the Second City's John Hancock Center has occasionally prompted horrific visions in his head.

"Every now and then I imagine that this is the view that people had from the World Trade Center, and I imagine how horrifying it would have been to have a plane coming right at you," he said. "From here, you can see the planes coming from miles away."

Richardson isn't alone. Though a full 12 months have passed since the attacks that felled one of the city's most visible symbols of success, many New Yorkers still struggle with the psychological fallout. And therapists said they expect to encounter more anxiety, depression and substance abuse this September as memories are triggered in what psychologists call the "anniversary reaction."

A month after Sept. 11, one in 10 people here was clinically depressed and 7.5 percent were experiencing post-traumatic stress disorder, according to a survey by the New York Academy of Medicine. The survey concluded that about a million New Yorkers suffered from one or both disorders in the weeks after the attacks.

Rachel Yehuda, an expert in the treatment of post-traumatic stress disorder at the Bronx VA Medical Center, said she still receives new patients plagued by memories of Sept 11. Other mental health professionals report ongoing anxiety and depression among their patients over Sept. 11 and terrorism in general.

But it's not just New York that's suffering.

"It's different for everybody now," said Marcia Kraft Goin, a psychiatrist at the University of California, Los Angeles. "It's continuous."

Though the effects are harder to assess in other parts of the country, where little research has been done since the immediate aftermath of the attacks, experts believe that the continued threat of terrorism is contributing to anxiety and depression across the nation.

Adults and children around the world saw graphic television footage of airplanes smashing into buildings, burning towers collapsing into rubble and people leaping to their deaths to escape the flames.

"People saw it over and over and over again," Goin said. "That added to the sense of trauma."

There is debate about whether televised images themselves can trigger post-traumatic stress disorder and other illnesses. Columbia University epidemiologist Christina Hoven said she heard reports of children as far away as Chile being troubled by the attacks.

Doctors in Pittsburgh treated an 11-year-old boarding school student who developed post-traumatic stress disorder and depression after watching television coverage of the World Trade Center. The boy became so upset that he threatened suicide five weeks after the attacks, doctors reported in the Journal of the American Academy of Child and Adolescent Psychiatry.

In New York City, even time could not heal all wounds.

By February, the number of people with clinical depression or post-traumatic stress disorder had dropped by one-half to two-thirds, still higher than epidemiologists would normally expect in a city as big as New York. One person in three continued to report at least some symptoms of depression or post-traumatic disorder, even if they did not fit the criteria for the illness itself.

Mothers of young children are especially anxious about the prospect of future terrorist attacks, said New York psychiatrist Julie Holland. They worry most about who will take care of their children if they die.

The children suffer too. Hoven has been studying schoolchildren in New York City to see if they have lasting emotional problems related to the attacks. Her results indicate that children from all over the city, not just in the immediate Ground Zero area, are suffering.

In February and March, Hoven surveyed 8,000 New York public school students in grades 4 to12. The questionnaires were designed to identify a broad range of ills, including depression, post-traumatic stress disorder and substance abuse.

Not surprisingly, Hoven found more problems among children who had lost relatives in the attacks or who knew somebody who had been at the World Trade Center on Sept. 11. But she also found a startlingly high incidence of psychological problems among children who did not have any special connection to ground zero.

"It was an event of such proportion that children were just overwhelmed with it," Hoven said. "You smelled it, you felt it, the subways were backed up, your parents couldn't go to work."

Adults and children who are suffering are now even more vulnerable to additional psychological damage, experts say.

"These people are actually at greater risk of developing psychological symptoms if something else happens," said Sandro Galea, an epidemiologist at the academy's Center for Urban Epidemiologic Studies.

And patients will not be the only ones struggling.

"Those of us who are trying to be the treaters have also obviously been affected by the experience, whether we were there or we weren't there," Goin said. "This uncertainty is so ever-present. And we can't forget it."

The Associated Press contributed to this report.