  The equations of motion of two point masses have recently been derived at the
3PN approximation of general relativity. From that work we determine the
location of the innermost circular orbit or ICO, defined by the minimum of the
binary's 3PN energy as a function of the orbital frequency for circular orbits.
We find that the post-Newtonian series converges well for equal masses. Spin
effects appropriate to corotational black-hole binaries are included. We
compare the result with a recent numerical calculation of the ICO in the case
of two black holes moving on exactly circular orbits (helical symmetry). The
agreement is remarkably good, indicating that the 3PN approximation is adequate
to locate the ICO of two black holes with comparable masses. This conclusion is
reached with the post-Newtonian expansion expressed in the standard Taylor
form, without using resummation techniques such as Pad\'e approximants and/or
effective-one-body methods.
