Microscopic black holes are sensitive to higher-dimension operators in
the gravitational action. We compute the influence of these operators
on the Schwarzschild solution using perturbation theory. All (time-re
versal-invariant) operators of dimension six are included (dimension-f
our operators do not alter the Schwarzschild solution). Corrections to
the relation between the Hawking temperature and the black hole mass
are found. The entropy is calculated using the Gibbons-Hawking prescri
ption for the Euclidean path integral and using naive thermodynamic re
asoning. These two methods agree; however, the entropy is not equal to
1/4 the area of the horizon.