To simplify the expression \(-10\sqrt{3} + \sqrt{27}\), we first simplify \(\sqrt{27}\).
\[ \sqrt{27} = \sqrt{9 \cdot 3} = \sqrt{9} \cdot \sqrt{3} = 3\sqrt{3} \]
Now, we can substitute \(3\sqrt{3}\) back into the expression:
\[ -10\sqrt{3} + \sqrt{27} = -10\sqrt{3} + 3\sqrt{3} \]
Next, we combine the like terms:
\[ -10\sqrt{3} + 3\sqrt{3} = (-10 + 3)\sqrt{3} = -7\sqrt{3} \]
Thus, the simplified expression is:
\[ \boxed{-7\sqrt{3}} \]