We studied the single photon ionization of gas phase 3-hydroxyisoquinoline by means of VUV synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer. Near the ionization thresholds of 3-hydroxyisoquinoline, the photoionization is found to occur mainly via a direct process. The spectra are assigned with the help of theoretical calculations on the equilibrium geometries, electronic states patterns, harmonic and anharmonic wave-numbers of the lactim and lactam forms of 3-hydroxyisoquinoline and their cations. The slow photoelectron spectrum (SPES) of this lactim is dominated by vibrational transitions to the (X) over tilde state of the cation. In addition, several weaker and complex bands are observed, corresponding to the population of the vibrational bands (pure or combination) of the (A) over tilde electronically excited state of the cation. The adiabatic ionization energy of 3-hydroxyisoquinoline and the lowest electronic state energetics of the lactim and lactam cationic forms are determined.