Longtime and frequent tipster Leonid Nemirovsky explains how to get adjacent hatch patterns in AutoCAD to match by adjusting their origin points.

"If you have a curved outline divided in the middle and cross-hatched in both areas and those patterns do not match, then select one piece of the hatch with a double-click. In the hatching dialog box, select 'Click to set new origin,' and select the point you want to match on the other piece of hatching. Now both pieces remain separate, but look like a single piece."
 
Notes from Cadalyst Tip Patrol: There are many ways to apply hatch patterns in a drawing. Sometimes you want to clearly identify to different areas. Sometimes you want that difference to be more subtle. Or maybe you don't want the paper copy to look any different.

For example, let's say you used two separate hatch patterns to help find an area in square units. If you want them to look the same, or at least to have their patterns aligned, move the hatch origin of one of them until they do line up. (The hatch origin is the starting point of the pattern; AutoCAD draws the defined pattern from that point. If you move the starting point, the rest of the pattern moves with it.)

In AutoCAD 2011, Autodesk gave us the ability to move a hatch pattern's origin with grips. This edit just got a lot simpler.