Minimal example:
\begin{table}[H]
\centering
\begin{tabular}{|l|c|c|}
\hline
Text A & Text B & Text C\\
\hline
& \multirow{2}{*}{\rotatebox{90}{Gewichtung}} \\
\hline
& & \\
\hline
A & 1 & 100 \\
\hline
B & 2 & 100 \\
\hline
\end{tabular}
\end{table}
If I use it like this, the text of the rotatet cell goes in another cell. So the cell doesnt get bigger. If I use:
\begin{table}[H]
\centering
\begin{tabular}{|l|c|c|}
\hline
Text A & Text B & Text C\\
\hline
& \rotatebox{90}{\multirow{2}{*}{Gewichtung}} \\ \hline
& & \\
\hline
A & 1 & 100 \\
\hline
B & 2 & 100 \\
\hline
\end{tabular}
\end{table}
it looks better. But how do I get the text "Gewichtung" centered now? Its a bit more right and on the top of the box.

\multirowis correctly interpreted to allow for spanning of multiple rows. In the second example,\multirowis completely ignored (notice howGewichtungonly spans one row). Since you seem to "prefer" the second - which doesn't require\multirowat all, what is it you're after exactly? You could even consider making a drawing of the table and including that in your post... – Werner Jul 22 '12 at 14:01