"Mask" is a tear-jerker in the sense that your dentist is a tooth jerker -- it yanks on your heart with pliers. That said, the story it has to tell is so unutterably sad and inspiring that the movie works in spite of itself. This is real get-out-your-handkerchief stuff, sure to melt the stoniest of cynics.

The movie is based on the short life of Rocky Dennis, a California adolescent who suffered since early childhood from craniodiaphyseal dysplasia, which causes the skull to grow crazily out of proportion. Makeup designer Michael Westmore has brilliantly recreated the mask of "Mask," the grotesque brow ridges and vast domed forehead, the way Rocky's face was stretched and tortured by the renegade bone roiling inside it.

What's extraordinary about "Mask," though, is not the makeup, but the way Eric Stoltz, as Rocky, makes his disfigurement all but disappear in your mind -- you're captured by his spirit. In "Mask," Rocky's just a nice kid who collects baseball cards, does well in school and fantasizes about a motorcycle trip around Europe. His mother is a tough-talking moll (Cher) leading a loose life among a crew of bikers who adopt Rocky as one of their own. Set against this extreme milieu, and the horror of his own handicap, Rocky's essential ordinariness becomes something to celebrate -- "Mask" makes a romance out of just being nice.

Director Peter Bogdanovich has a good feel for the bikers' lunacy (they're less Hell's Angels than Heaven's Devils). There's a wonderfully anarchic scene at a bikers' picnic, where Rocky and his mom chat with friends while a huge brute named Dozer bashes his colleagues around in the background. In "Mask," suburban quiet exists only to be shattered by erupting mufflers and slammed doors. The movie needs more of this texture, and in its original cut, it had more -- two scenes, of a biker's funeral and of Rocky and his mom singing for the bikers, have been removed. The studio's instincts were right -- at over two hours, "Mask" is still way too long. But there's other fat that could have been trimmed instead -- Anna Hamilton Phelan's script is full of redundancies, as the same emotional and character points are made over and over.

Much of Cher could have been lost as well, with no damage to the movie. Halfway through, "Mask" veers out of control, as it begins to focus less on Rocky and more on his mom, who has a drug problem. Bogdanovich has some fun with mom's romance with Gar (Sam Elliott) -- they lock glances like adversaries in a spaghetti Western, and the charismatic Elliott takes the camera well. But usually when Hollywood talks about junkies, the result is, well, junk. The drug theme doesn't bring out the best in Cher. It's her occasion to do her Oscar turn, and her frazzled emotional displays actually seem nasty -- it looks as if she's trying to steal center stage from a deformed kid.

But Stoltz's performance is so winning, it almost doesn't matter. The challenge of the role is obvious -- layered with makeup, Stoltz can't show much expression. He has to rely on physical acting, the bouncy walk that expresses Rocky's innate good humor -- even the flip of his wrist when he bolts a door seems cheery. Rocky talks through his broken teeth (also deformed by the disease) in the private, quiet deadpan of a kid who's used to making an inside joke of the world that's locked him out. By the end, you're looking at the movie's flaws with the same upbeat nonchalance with which Rocky Dennis looked upon his own. Mask, opening today at area theaters, is rated PG-13; it contains profanity and sexual themes.