Gov. Jay Nixon signed legislation this month to require insurers to cover eating disorders beyond the point of a person getting back to a certain weight.
According to the National Eating Disorders Association, it's the first bill in the nation to define such treatment.
Advocates say patients with eating disorders are kicked out of treatment prematurely, having gained weight but not having the underlying mental issues addressed.
Insurance companies who provide coverage for Missouri residents have resisted such a change, saying it could mean higher costs. But they struck a compromise with lawmakers on language to cover "medically necessary" treatments.
The law will take effect in August.