The equilibrium structure and potential energy surface of beryllium monohydroxide in its ground doublet state, X(2)A' BeOH, have been determined from large-scale ab initio calculations using the spin-restricted coupled-cluster method, RCCSD(T), with basis sets of double- through quintuple-zeta quality. The BeOH radical was found to be quasilinear, with an equilibrium BeOH angle of 140.9degrees and a barrier to linearity of 136 cm(-1). The vibrational-rotational energy levels of various isotopomers were predicted using the variational method. The calculated spectroscopic constants should be useful in the future detection of beryllium monohydroxide by high-resolution vibrational-rotational spectroscopy.