Depending on how far the drop was, the manufacturer would recommend replacing it. After bashing someone in the face... it would prolly have to be hard enough to knock them out to do real damage to the helmet.
Your best bet, if you have doubts, is to take it to a hospital and have it x-ray'd for cracks. I hear that most will do it for free.
My last helmet was dropped several times before I got a new one.... I guess it depends on how much you value your head

 

From HJC's website.........

Dropped or crashed helmet

HJC strongly recommends immediately replacing a helmet that has sustained an impact in the case of a crash, regardless of the severity. Unseen damage (fractures) could occur to the outer shell or compression within the impact absorbing EPS liner which could severely hinder the impact absorbing capacities of the helmet.
HJC also recommends replacing a helmet that was dropped on any solid surface such as asphalt, concrete, rock, etc. from heights as low as 2'. As with a crash, unseen fractures could occur within the helmets outer shell that could severely hinder the impact absorbing capacities of the helmet.


http://www.hjchelmets.com/helmet_usage.htm

 

From HJC's website.........

Dropped or crashed helmet

HJC strongly recommends immediately replacing a helmet that has sustained an impact in the case of a crash, regardless of the severity. Unseen damage (fractures) could occur to the outer shell or compression within the impact absorbing EPS liner which could severely hinder the impact absorbing capacities of the helmet.
HJC also recommends replacing a helmet that was dropped on any solid surface such as asphalt, concrete, rock, etc. from heights as low as 2'. As with a crash, unseen fractures could occur within the helmets outer shell that could severely hinder the impact absorbing capacities of the helmet.


http://www.hjchelmets.com/helmet_usage.htm

Damn it.....I recently had my helmet on my handle bar when it fell off and hit the pavement. Does this mean I should check for cracks via x-ray?

 

I've got a buddy of mine that said the same thing...he does some racing and been riding for years. Any impact with a solid surface from over 2 feet should be checked and replaced.

Then again, they tell you to change your oil in your cage every 3K miles...I guess it is all in how much you value YOUR motor! lol Damn, that was a good analagy, huh? lol sorry, going back to sleep

 

if the fall wasnt bad at all i wouldn't replace it, the manfactures want you to replace it if you drop it so you can spend more money on their product, but safety first

 

MSF course showed what an impacted helmet does...... the inside is all hitech shit that looks like styrofoam..... so once it gets bruised or whatever, it loses its ability to spread the impact ... they are right when they say to get it checked out if its been dropped..... It aint worth it to be riding with a compromised helmet....