It sounds like something out of a horror movie, but wrong-sided surgery happens more often than you think.

Concerns about surgeons operating on the wrong part of the body made headlines after The Providence Journal reported that on three separate occasions this year, surgeons at Rhode Island Hospital operated on the wrong side of a patient’s head. The most recent case happened last Friday, when the chief resident started to cut on the head of an 82-year-old patient. The resident, a doctor in the seventh year of specialty training, realized the error before reaching the skull and closed the wound with a single stitch. The procedure was done on the correct side, “with good results,” according to a statement from the hospital, which was fined $50,000 by the state health department.

On a percentage basis, surgery on the wrong side or area of the body is considered rare. But nonetheless, it affects hundreds of people a year, and hundreds more cases likely go unreported. This month, the Archives of Surgery ran a letter from The Joint Commission, the primary accrediting agency for hospitals in the United States, noting that it receives about nine voluntary reports per month of so-called “wrong-site adverse events” to its Sentinel Event Database. Last September, the same medical journal reported that wrong-site surgery may be underreported by a factor of 20. That study concluded that there are 1,300 to 2,700 wrong-site procedures annually in the United States.

Read the New York Times story