Milkshake fans, it’s time once again to count your lucky straws.

In 1967, a McDonald’s franchisee whipped up a minty shake as a special St. Patrick’s Day treat for his customers in Enfield, Conn. Now, nearly 50 years later, customers across North America await the annual return of the beloved emerald green dessert known as the Shamrock Shake just as winter starts to loosen its grip.

“Every year around this time, my family and friends start asking me when we will bring back the Shamrock Shake,” said McDonald’s archivist Michael Bullington. “For many, it’s a rite of spring.”

The limited-edition shake usually appears by March 1st and is gone soon after those green sweaters and scarves return to their closets. The treat has built a cult-like following of loyal fans who welcome a temporary addition to the vanilla-chocolate-strawberry lineup. Many, in fact, have lobbied the Golden Arches to promote the Shamrock Shake from seasonal offering to permanent fixture on the McD’s menu.

In 1970, the shakes were introduced in select U.S. markets as the “St. Patrick’s Day Green Milkshake” before later adopting the now-iconic moniker. Due to popular demand, the shakes went nationwide in 2012 and are also available in Canada and Ireland.

The frozen favorite has inspired the launch of Facebook fan pages, blogs, online discussion groups -- and even a few copycat recipes. “It offers something completely different for your taste buds,” Bullington explains. “We’ve had seasonal flavors come and go, but the Shamrock Shake has always been a customer favorite.”

A Legacy of Love

In 1974, the Shamrock Shake crated a legacy that extends well beyond the dessert menu. Philadelphia Eagles star Fred Hill's 3-year-old daughter, Kim, was being treated for leukemia at Children's Hospital of Philadelphia. Hill and his wife, Fran, camped out on hospital benches and sat in cramped waiting rooms during Kim's three years of treatment. They met many parents and families who’d traveled great distances so their children could receive medical treatment. Few could afford hotel rooms.

Determined to come up with a solution, Hill rallied the support of his teammates. Eagles GM Jim Murray offered the organization's support to Dr. Audrey Evans, head of the pediatric oncology unit at Children's Hospital of Philadelphia, who had long dreamed of a "home away from home" for families of children being treated at the hospital.

Murray called Don Tuckerman, a friend from the local McDonald's advertising agency, to inquire about his next planned promotion in the Philadelphia area. "St Patrick's Day," Tuckerman told her. "Shamrock Shakes."

The milkshakes and the Eagles happened to share the same color -- green -- creating the perfect combination for a local campaign. So, with the support of McDonald's founder Ray Kroc and regional manager Ed Rensi, Tuckerman launched a week-long promotion with all Shamrock Shake profits going to the cause.

They raised enough funds to help buy a four-story, seven-bedroom house near the Children's Hospital of Philadelphia. Later that year, it opened as the first Ronald McDonald House. The network of houses quickly grew across the country and, eventually, around the world. Families can now stay together close to where their child is being treated, and be comfortable and cared for during their stay.

“Today there are 336 Ronald McDonald Houses in 35 countries,” Bullington adds. “Most people probably don’t realize the Shamrock Shake had a hand in making such a great idea a reality.”