We present deep JHK photometry of the old and metal-rich open cluster NGC 6791 .
The photometry reaches below the main sequence turn-off to K \approx 16.5 mag .
We combine our photometry with that from Stetson , Bruntt , & Grundahl ( 2003 ) to provide color-magnitude diagrams showing K vs . J - K , K vs . V - K , and V vs . V - K .
We study the slope of the red giant branch in the infrared , but find that it is not a useful metallicity indicator for the cluster , nor any metal-rich cluster that lacks a well-populated red giant branch , because it is not linear , as has often been assumed , in K vs . J - K .
The mean color of the red horizontal branch/red clump stars provide an estimate the cluster reddening , E ( B - V ) = 0.14 \pm 0.04 mag for [ Fe/H ] = +0.4 \pm 0.1 .
The mean magnitudes of these stars also provide a good distance estimate , ( m - M ) _ { 0 } = 13.07 \pm 0.04 .
Finally , we find that the isochrones of Yi , Kim , & Demarque ( 2003 ) provide optimal fits in V vs . B - V and V - K and K vs . J - K and V - K for such values if [ Fe/H ] lies between +0.3 and +0.5 ( with a slight preference for +0.5 ) and ages between 9 Gyrs ( [ Fe/H ] = +0.3 ) and 7.5 Gyrs ( [ Fe/H ] = +0.5 ) .