For many patients, the law means insurers will no longer be allowed to refuse to pay for office visits because the doctor is a psychiatrist instead of an internist, or charge more for prescriptions that treat depression than for medicines that treat heartburn.

"This truly represents a great leap forward," said Gov. Christine Gregoire, who signed the bill into law. "When we fail to treat mental illnesses in the same way we treat illnesses of the body, it costs everybody."

Patient advocates and hospitals have been fighting for the law for nearly a decade.

In Washington, some insurance policies don't cover mental health treatment. Others provide coverage, but with weaker terms than for medical or surgical coverage. For example, some limit the length of hospital stays they will reimburse if the admission is for psychiatric treatment. Some businesses said they couldn't afford to give their workers health coverage unless they drew that distinction.

But insurers will now be required to provide so-called mental health parity, according to the measure Gregoire signed.

Although employers are not required to provide their workers with insurance benefits, many state programs and larger companies that do so will have to include mental health treatment.

Sally Stultz of Spokane Valley said her 17-year-old son is diagnosed with brain damage and bipolar disorder. She said her family's insurer quickly cut off coverage after her son's condition took a dangerous turn more than a year ago. He was skipping school, running away and even shoplifting.

"He was, frankly, headed toward life on the streets," she said. "He was careening out of control. I maxed out my mental health insurance on him in one month's (hospital) stay because I was just desperate to find something to help.

"Had he had the kind of coverage he needed early on, he probably would have been in a whole lot better shape today," she said, adding that such coverage also would have saved taxpayers in educational and social services her son now receives.

Some businesses have predicted this measure will force them to drop coverage for their employees. And over the years, supporters of the measure have made substantial concessions. Policies bought by individuals or through employers with 50 or fewer workers will be exempt from House Bill 1154, which will be phased in between 2006 and 2010.

"That's a problem," Stultz said. "There are going to be a lot of people who lose out. And, of course, there's all the downstream effects (of inadequate mental health care)."

Backers of the bill say untreated mental illness leads to reduced productivity for some workers - and prison sentences for others. As part of his condition, Stultz's son suffers from memory problems that contribute to him making the same mistakes repeatedly, Stultz said.

"Early on, if a lot of folks got what they needed, they might not end up critical and in the jails," she said. "It's inhumane, as far as I'm concerned. These folks, they don't need prison; they need help.

"I feel like it's a measure of society - how much a society is willing to take care of its own."

Many large employers are exempt because they use so-called "self- insured plans," in which the employers cover the cost of care. More than one-fifth of Washington policies are such plans, which are not regulated by the state.

The two sides of the debate disagree over how much it will cost.

Backers of the measure claim it will boost insurance costs by a net of 0.44 percent after employers offset some of their expenses through rate increases and benefit reductions. Opponents say it will increase costs by 2 percent to 5 percent. And state budget officials estimate it will increase taxpayer-supported health costs by nearly $9 million a year when fully implemented.

The Insurance Commissioner's Office estimates 1.6 million Washingtonians are covered by policies that will be subject to the new rule.

"It (won't) solve everything," Stultz said, "but I know it would have made a difference for my son."

P-I reporter Chris McGann contributed to this report, which includes information from The Associated Press.

P-I reporter Angela Galloway can be reached at 206-448-8333 or angelagalloway@seattlepi.com