“一年一度圣诞节”是“动物圣诞节”的一首歌，总共唱了三次。第一次在开头，第二次在圣狮幼崽学习堕胎知识的时候，第三次作结尾曲。
背景
这首歌的旋律取自1974年定格动画《没有圣诞老人的那一年》（The Year Without a Santa Claus）里面的歌曲“我相信圣诞老人”（I Believe in Santa Claus）。
经过旁白的提示之后，斯坦带着圣狮幼崽们来到意外怀孕诊所学习堕胎知识，这样就可以把敌基督流产掉，让森林小动物的邪恶计划流产。在学习知识的时候，这首歌就是背景音乐。
在故事结局之后，这首歌也作为片尾曲又放了一次。
南方公园：真理之杖
在意外怀孕诊所给兰迪做堕胎手术的时候，以及最后来到奴隶先生肚子里的尽头的阴道核弹做堕胎手术关闭核弹的时候，新来的会在这首歌的旋律中玩堕胎手术小游戏。
歌词
First Version:
Christmas time is once a year.
Every critter holds it dear.
Every animal big or small,
Christmas means so much to us all.
Second Version:
Christmas time is once a year.
Every critter holds it dear.
Every animal big or small,
Christmas means so much to us all.
It's once a year, it's Christmas time!
And it happens once a year.
It's once a year, it's Christmas time!
When we hear about how Christmas only comes
Once a year.
Third Version:
Christmas time is once a year.
Every creature holds it dear.
Every animal big or small,
Christmas means the world to us all.
It's once a year, it's Christmas time!
When we hear about how Christmas only comes
Once a year.