How likely am i to have sickle cell disease?

Impossible to say: Without knowing anything about you, i can't say how likely. Any symptoms previously or family history? If not, much less likely. Ancestors from africa or around the mediterranean? If not, much less likely. Were you born in a state after they had required screening for sickle cell? If yes and your parents were notified that your screen was normal then you don't. I can't help much more than that.