  We report on X-ray observations of the solitary 4.8 ms pulsar PSR J0030+0451.
The pulsar was one of the last targets observed in DEC-98 by the ROSAT PSPC.
X-ray pulses are detected on a $4.5\sigma$ level and make the source the
$11^{th}$ millisecond pulsar detected in the X-ray domain. The pulsed fraction
is found to be $69\pm18%$. The X-ray pulse profile is characterized by two
narrow peaks which match the gross pulse profile observed at 1.4 GHz. Assuming
a Crab-like spectrum the X-ray flux is in the range $f_x= 2-3\times 10^{-13}$
erg s$^{-1}$ cm$^{-2} $ ($0.1-2.4$ keV), implying an X-ray efficiency of
$L_x/\dot{E}\sim 0.5-5 \times 10^{-3} (d/0.23 {kpc})^2$.
