Start by popping the popcorn and transfer it to a large bowl.
Add the sugar and karo syrup to a pan over medium heat. Stir until the sugar melts and the mixture begins to boil.
Once it boils, take it off the heat and add the peanut butter and vanilla. Stir until peanut butter has melted and the mixture is smooth.
While the mixture is still hot, pour it over the popcorn and stir until evenly distributed. Enjoy while it is warm or when it has cooled down!