Stamp Out Diabetes Act of 1998

Stamp Out Diabetes Act of 1998 - Amends Federal law to require the Postal Service to establish a special rate of postage for first class mail that is up to 25 percent higher than the regular rate as a voluntary alternative that the public may use to contribute to funding for diabetes research.

Requires collected amounts to be paid to the National Institutes of Health (NIH).

Expresses the sense of the Congress that nothing in this Act should: (1) cause a net decrease in total funds received by NIH below the level that would have otherwise been received but for this Act's enactment; or (2) affect first-class or other regular postage rates.

Requires special postage stamps to be made available to the public.

Terminates this Act two years after such stamps are first made available.