Magnetotransport experiments on a semiconductor quantum ring in the Coulomb blockade regime are described. The measurements allow to extract the discrete energy levels of a realistic ring, which are found to agree well with theoretical expectations. The interaction effects important for our ring structure are analysed in detail. The experimentally observed charging energy can be quantitatively understood within the Hartree approximation including a strong screening contribution due to the top gate. The strong screening effect is the reason for the frequent occurrence of spin-pairs in the addition spectra. The relation of the observed addition spectra to persistent currents is established and the magnitude of the current is extracted from experimental data.