i can't believe everybody thinks this is rare.... the concept started in Pokemon Crystal, and was supposedly more common for the female players. i always play as a female, and i have gotten it so many times, i haven't considered it as rare. i haven't played a pokemon game yet that i didnt get it at some point before the fourth badge naturally. i got it from my first bunnelby i caught starting in y the first time, for petes sake. here's a gift: i'll just start spreading to my multiples of bred castoff pokemon and trade them over wonder trade. if you get one from Anemone with piggy tails and the purple exotic hat, voila, enjoy the start of the pokerus parade. one last note, though. contrary to one of the answers, the effect fades after the face pops up and the pokemon is cured, not continues. also, it has no effect in super training, making it almost useless now. but if it makes people happy, i'm perfectly happy to spread it around. the illness does last longer with traded pokemon....