Worcester, Massachusetts is incorrectly spelled "Worchester" in the film.
It is stated that Burt Baskin died at age 51 of a heart attack; he actually died at age 54.
When Morgan was stating the 7 things on the McDonald's menu that don't contain sugar, the fries and hash browns turn into blood sugar, and Diet Coke has Aspartame, which is a sugar alternative.
Although a calorie is the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius, a food Calorie is actually a kilocalorie (aka "kilogram calorie" or "large calorie"), so the nutrition expert's definition is correct in this context.
When the movie shows McDonald's locations worldwide, 2 golden arches were shown in the country of Iceland. However, many people know Iceland to be a country with no McDonald's restaurants. The film, however, was released in 2004 and McDonald's didn't close its Reykjavic restaurants until 2009. So it was correct at the time.
Near the end, when Morgan Spurlock says, "Why not do away with your Super Size options?", the water condensation runs up the drink.
When Morgan is in the car with the Super Size meal, as he shows the camera the big box of fries, before the picture zooms in, someone in a green jacket with a scarf knocks on the car window and waves.
When the French woman is talking about drinking Super Sized Cokes at McDonald's in France, as she says "even the small size here, I can't drink", the picture flips to a mirror image.
"The Wacky Adventures of Ronald McDonald" is erroneously referred to as a "cartoon on TV." It was actually a series of direct to video specials released at McDonald's restaurants between 1998 and 2003.