  We report the first determination of the binary period and orbital ephemeris
of the Be X-ray binary containing the pulsar 1A 1118-616 (35 years after the
discovery of the source). The orbital period is found to be Porb = 24.0 +/- 0.4
days. The source was observed by RXTE during its last large X-ray outburst in
January 2009, which peaked at MJD 54845.4, by taking short observations every
few days, covering an elapsed time comparable to the orbital period. Using the
phase connection technique, pulse arrival time delays could be measured and an
orbital solution determined. The data are consistent with a circular orbit, and
the time of 90 degrees longitude was found to be T90 = MJD 54845.37(10), which
is coincident with that of the peak X-ray flux.
