Using data recorded by the CLEO II detector at the Cornell Electron St
orage Ring, we report the first observation of an excited charmed bary
on decaying into Xi c(0) pi(+). The state has mass difference M(Xi(c)(
0) pi(+)) - M(Xi(c)(0)) of 174.3 +/- 0.5 +/- 1.0 MeV/c(2), and a width
of <3.1 MeV/c(2) (90% confidence level limit). We identify the new st
ate as the Xi(c)(+), the isospin partner of the recently discovered X
i(c)(0).