If you think raw fish should be used for bait only, skip this section. But if you just love the slippery succulence of sashimi, order on; your risk is low. Discounting the possibility of mercury in fatty fish like tuna, the chances of getting sick from a sushi-borne parasite in the U.S. are slim. That's because almost all of the sushi-grade fish sold here is previously frozen, which generally kills parasites.
However, this doesn't account for the fingers that prepare it, improper storage or restaurant contaminants. The rule of thumb: If there's something fishy about your sushi—if it looks or smells bad—don't eat it.