Under obamacare, can you wait to buy insurance until after getting sick or does it have to be done prior?

Don't wait to enroll: There will be an "open enrollment" period from oct 2013 through March 2014 at Covered California, the marketplace for California. If a person waited until after March to enroll, she might not be able to get insurance for 2014 through the marketplace, unless she had some special circumstances (such as losing her job, birth of a new baby, or death of a spouse).