How do I know if I have got stitch?
Typically, stitch is felt in the right upper abdomen, but may also occur on the left hand side, or may irradiate to upper or lower regions of the body. "Classic" stitch is more likely to occur to insufficiently trained people than well prepared athletes.

What causes Stitch?
The reason for stitch is pretty simple. The inner organs are hanging from several ligaments, which, in turn, are fixed to the diaphragm, the muscular "plate" between chest and abdomen. Liver, spleen, stomach, small intestine and colon form a weight of several kilograms, hanging from the diaphragm. The impact of every step forces the inner organs to move downwards. Additionally, the diaphragm moves upwards on every expiration to force air out of the lungs. This continuous up/down stress may cause a cramp in the diaphragm: stitch. Stitch occurs most often on the right hand side because of the liver being the most heavy organ, and therefore the one stressing the diaphragm the most.

How do I get rid of Stitch?
Should you suffer from stitch, the first (and best) cure is to slow down or stop until the stitch is gone. If you do not want to stop, you can try to press your hand onto the part of your abdomen where the stitch is, and release the pressure on expiration. Repeat this several times. The advanced method requires some thoughts about the reason why stitches occur. You should try to synchronise your breathing pattern with your running, and exhale when the foot on the not hurting side touches the ground, i.e. when you have stitch in your right hand side, try to exhale when your left foot touches the ground. You do not need to worry about inspiration - if your expiration is right, your inspiration will be, too. If you manage to keep this breathing pattern, your diaphragm moves downward at the same time as your intestines, thus decreasing the stress.

How can I avoid Stitch?
Strengthen your abdominal muscles, keep your upper body warm, do not run too soon after meals and learn "abdominal breathing"

Thanks Valley Boy. A useful and informative read.

Cheers,
Dave