some things are just better left in the darkness, hidden deep away from certain people, this is one of those subjects that should pretty much always be left in the shroud we'll call 'saftey'....

btw, alot of people feel guilty about marijuana usage, that doesn't mean you should tell people... just the opposite usually... but as said 2x before me, only you know your parents and only you could really judge whether you should tell them or not... most likely tho, depending on your age, they will find out, or atleast get suspicous at one point or another, this by no means should be taken as a time to come clean, alot of times you're setting yourself up for failure...

in the end, as always it's your decision, my input is no, dont' tell them, you should really never incriminate yourself for anything. i told my grandma, who is the one that raised me, only problem she had with it, is it was illegal, but alot of parents aren't as open minded about things as she was with me growing up.