After reading the thread about the hiker who died in the Grand Canyon, I reflected on my greatest concerns while hiking. I concluded that there are really only three:
Dehydration -- A lot of the places I hike are hot and dry. Making sure I have enough water is always near the top of my list of concerns.
Falling -- Perhaps it is because I took a nasty fall a few years ago, but I often think about how long it will take to be found if I take a fall off the edge of the trail.
Hypothermia -- I don't hike a lot in the winter, but start early in the spring and into the fall. I pay attention to staying warm and dry.
What are your fears when hiking?