This is pretty accurate:

To cover their own butts, doctors sometimes take a needless trip up yours. A nationwide sample of “surveillance” colonoscopies–follow-up procedures done after polyps are removed–found that up to 50 percent of doctors recommended these tests unnecessarily. This better-safe-than-sorry mindset keeps docs safe against lawsuits, and isn’t limited to colonoscopies.

Get the truth: Watch out for the most overused procedures: MRIs and CT scans, echocardiograms, and stress tests all scored high in a survey of health insurers. “When your doctor does make a recommendation that seems aggressive, ask why, and where you fit in the assigned guidelines,” says Pauline Mysliwiec, M.D., author of the colonoscopy study.