[giantg2]

In general, the rule of thumb is to never eat any mushrooms raw. But there are a few exceptions, including button mushrooms. I won't eat raw mushrooms, except maybe truffles (if you really cook truffles then what's the point?).

[s1artibartfast]

I think you mean button mushrooms are no exception.

[giantg2]

They are a common exception. I wouldn't eat them raw though.

[inferiorhuman]

Portabellos and button mushrooms are the same damn thing.

[giantg2]

And they are both currently, wide spread exceptions. Food safety bodies do not require them to be cook, their raw use is widespread, some mushroom experts still say it is ok, etc. The status quo has not yet changed.