Let $Q(R)$ denote the quotient field (or field of fractions) of an integral domain, $R$.
If $R$ and $S$ are integral domains such that $Q(R)\cong Q(S)$, does this imply that $R\cong S$?
I am not sure about this. I was thinking the answer is yes, but I couldn't prove it. Perhaps there exist a counterexample?
No.
Hint: Think about $\Bbb Z$ and $\Bbb Z[\frac12]$, for example.