It depends on your health insurance policy. Some plans cover Viagra, and some don't.
Coverage of Viagra, in fact, sparked controversy after the drug was patented in 1998. In some cases health insurance plans covered the sexual dysfunction drug for men, but did not cover contraceptive pills for women, leading critics to charge discrimination.
That's not as much the case anymore. Twenty-nine states have passed laws mandating group health plans cover prescription contraceptive drugs and devices, according to the "Health Insurance Mandates in the States 2010," by the Council for Affordable Health Insurance. No states mandate group plans to cover erectile-dysfunction drugs.
Check your health plan's prescription drug coverage to see if it covers Viagra. Keep in mind the patent for Viagra will expire in 2012, opening the way for more-affordable generic versions of the popular drug.
For more, see health insurance basics.