Despite his celebrity, no one has noticed the secret Michael J. Fox has kept for the past seven years -- that he's suffering from the incurable, debilitating Parkinson's disease.

The Canadian-born actor hopes to continue working in TV and film despite the progressive neurological disease, perhaps best known as the ailment that's handicapped former boxing sensation Muhammad Ali for several years.

Fox, 37, stars in the sitcom Spin City. He rose to fame in TV's Family Ties and has made several feature films. He's married to actress Tracey Pollan. They have three children.

In a People magazine cover story, in the issue to hit news-stands tomorrow, Fox discusses the impact of Parkinson's. He's had brain surgery to help control physical tremors and is being treated with experimental drugs.

Fox was diagnosed in 1991 and the disease has progressed in recent years. His neurologist told the magazine that Fox is in the "late mild stage" of the disease.

Parkinson's destroys dopamine in the brain, a chemical which controls motor functions. It generally strikes people much older than Fox.