Most R-rated comedies involve meaningless sex. “The Sessions” is the rare one about meaningful sex.

For Mark O’Brien (surefire Oscar nominee John Hawkes), intimate relations are nearly impossible. The 30-something poet and journalist has remained dependent on an iron lung since contracting polio at age 6. Bent like a question mark, the paralyzed Mark makes brief forays into public on his motorized gurney, but for the most part he spends his days in isolation. It’s not the greatest setup to meet women.

Although the subject matter is profound and moving in this based-on-a-true-story character piece, “The Sessions” offers as much humor as drama.

The deeply religious Mark confides to hipster priest Father Brendan (William H. Macy) that the clock is ticking on losing his virginity. So he ponders consulting a surrogate. Since sex before marriage is a sin within the Catholic church, the priest faces a challenge on how to counsel this decision.

Father Brendan asks, “What’s the difference between a sex surrogate and a common prostitute?”

Mark responds, “I don’t know, but I think there’s a difference.”

Technically, a surrogate engages in physical relationships with patients to achieve therapeutic goals. But as “The Sessions” illustrates, these interactions aren’t always consummated without some emotional fallout.

This Sundance Festival winner is a showcase for Hawkes (“Winter’s Bone”), whose acting style typically provides a model of restraint. He portrays Mark as witty, sincere and vulnerable, an immensely likable character. Although the man’s condition leaves him unable to be anything but horizontal — a real challenge from a filmmaker’s standpoint — his personality proves ascendant.

Equally impressive is Helen Hunt, who plays professional surrogate Cheryl. She’s a married mom in her late 40s who works with physically impaired patients, and she approaches “body awareness techniques” with a mix of clinical detachment and hippie abandon. While her philosopher husband (Adam Arkin) considers her a saint for this vocation, he is also unwilling to have such work follow her home.

Hunt is being commended for embracing the stark sexuality/nudity of the role, but it’s her empathy that is so striking (even if her Boston accent comes and goes). She just plain “gets” how important the experience is for this man, and she conveys it with subtle clarity.

A poignant short documentary titled “Breathing Lessons: The Life and Work of Mark O’Brien” deservedly won an Oscar in 1997. “The Sessions” arrives at some of the same truths, yet journeyman writer/director Ben Lewin — also diagnosed with polio at age 6 — finds heartfelt comedy in this decidedly raw material.

“Is this your place?” Cheryl asks during their first appointment.

“No, it’s a friend’s,” Mark replies. “The only bedroom furniture I have at my place is an iron lung. I’ve been wondering about possibly buying a futon, you know, in case the need arose.”

It’s a delicate balancing act, indeed. In lesser hands the project could have been crude or sentimental, or even accused of pandering to the academy. Lewin takes the no-frills approach and delivers it with such earnest intentions that even audience members uncomfortable with the blunt subject matter will likely respond with enthusiasm.

Lewin and his stellar cast transform “The Sessions” into the unlikeliest crowd pleaser of the year.

(At the Glenwood Arts, Studio 30 and Tivoli.)