The study found that those who were spanked or slapped had increased rates of anxiety disorders, anti-social behavior and depression.

But the authors of the survey of 4,888 adults in Ontario were quick to add that once spanked a child wouldn't automatically develop problems.

``Not everyone who is spanked or slapped (as a child) goes on to develop a disorder,'' said Dr. Harriet MacMillan, who developed the study with five other researchers at McMaster University in Hamilton, Ontario.

Their study, published on Tuesday in the Canadian Medical Association Journal, is believed to be the largest of its kind in the world.

The researchers based their findings on the responses of adults, ages 15 to 64. Of the respondents who were slapped or spanked occasionally, 21 percent developed anxiety, 7 percent suffered from major depression, 13 percent had an alcohol problem, and 17 per cent developed drug abuse or an anxiety disorder.

``It is likely that some, but not all (respondents), are at risk for developing a disorder,'' she said. ``But since I can't predict who will develop a disorder, the risk should be avoided by practicing alternative forms of discipline.''

About 70 to 75 percent of Canadian parents spank their children, according to previous studies. But 41 percent of those surveyed were ``rarely'' spanked or slapped as children, while 34 per cent said ``sometimes'', 21 per cent said ``never'' and 6 per cent responded ``often''.

But spanking is much more common in society than the data indicates, because kids are mostly frequently spanked between the ages of 3 and 4, and that is too early for most adults to remember, MacMillan said.

She hopes her findings will encourage parents to avoid spanking as a disciplinary tool.

The Toronto-based legal-aid clinic, Justice for Children and Youth, is launching a constitutional challenge against spanking.

"The study reinforces what parents need to hear - spanking is is not good for children and parents need to modify their behavior, said lawyer Cheryl Milne.