It might seem simple — a molded boneless pork patty served on a toasted bun and topped with onions, dill pickles and barbecue sauce — but the McRib is a powerhouse.

“The McRib is a very popular seasonal item like the Shamrock Shake,” said Leslie Holbrook, a McDonald’s spokeswoman.

(That leprechaun-colored shake with a cult following has been sold at McDonald’s restaurants around the St. Patrick’s Day holiday since 1970.)

Updated figures weren’t available, but the popularity of the sandwich helped McDonald’s Corp. sales figure rise 4.8 percent in Nov. 2010, although the McRib has been elusive in previous years.

The sandwich has become legendary, and has its groupies.

There are online McRib locators to help fans find the sandwich in certain areas.

According to Yahoo.com , the McRib was first introduced in 1981, but disappeared in 1995. It has resurfaced sporadically since 1994 and not always at every location at the same time.

A Dec. 5 press release announced the sandwich would once again hit this market early next year.

It will be available “through January while supplies last,” Holbrook said.

McDonald’s is promoting the McRib hard.

Click here for 101 reasons the chain says you should eat the sandwich.

Sandwich nutrition facts:

Calories - 500

Total Fat - 26g

Carbs - 44g

Protein - 22g

Sodium - 980mg

What do you think? Are you a McRib fanatic?