Sex and disability are murky waters for film. How does a filmmaker depict sex involving disabled people without gawking or needlessly inflating the significance of the event? How to show it as both normal and meaningful?

These questions apply, of course, anytime filmmakers put sex on the screen, but the risks of picketers are lower when you've got pretty, able-bodied stars shaking the sheets. Films about people with disabilities often omit sex entirely—consider My Left Foot or The Diving Bell and the Butterfly. Scarlet Road, a recent documentary about an Australian sex worker who specializes in clients with disabilities, is undoubtedly sex-positive and determinedly non-voyeuristic, but celebrates the central sex worker as a goddesslike savior for her clients.

So I approached The Sessions with generous skepticism. The drama is based on the true story of Mark O'Brien, a polio survivor and writer who spent most of his life in an iron lung. At age 38, he decides to lose his virginity and hires a sex surrogate to guide him through the deed. But rather than glorifying sex or treating it with clinical coldness, writer-director Ben Lewin charts Mark's quest with grace, warmth and wry humor. Explicit nudity (female only, thanks to the MPAA's double standard) has never been so moving and delicate.

As Mark, the versatile John Hawkes—recently seen as a menacing meth addict in Winter's Bone and a sinister cult leader in Martha Marcy May Marlene—turns in an astonishing performance. Hawkes spends the entire film on his back, his head cranked at a 90-degree angle and his spine contorted, but his wheezy voice and expressive eyes convey deep wells of pain and self-consciousness along with biting wit.

Mark's droll and sardonic one-liners pepper The Sessions. When asked if he's religious, he answers in the affirmative: "I find it absolutely intolerable not to be able to blame someone for all of this." At one point, Mark's caretaker asks him for a favor. "What, you need help moving furniture?" he asks. The scenes with the sex surrogate, Cheryl, played with bravery and guarded emotion by Helen Hunt, are surprising and affecting. In an NPR interview, Hawkes noted that he and Hunt filmed their scenes chronologically. This is apparent in the palpable discomfort of Mark and Cheryl's first sessions: She must undress him without his help, and he unintentionally ejaculates. (Lewin, to his great credit, does not turn this into a joke.)

The Sessions is unapologetically uplifting and flush with lyrical snatches of language. There's also a fantastic turn by a shaggy-haired, tan-skinned William H. Macy as Mark's priest, who undergoes a mini-crisis of faith as he blesses the whole sinful endeavor. Lewin could have stood to give the film sharper teeth—his characters seldom show frustration or anger—but he also, mercifully, does not paint them as faultless saints. And as central as sex is to The Sessions, Lewin takes a balanced view: Is the act wholly earth-shattering? Perhaps not. But exciting, important, maybe even therapeutic? Yes—much like this film. R. 

Critic's Grade: A-

SEE IT: The Sessions opens Friday at Fox Tower.