Observations of the spectroscopic binary a Vir have been made with the Narrabri stellar intensity interferometer in 1966 and 1970. It has been shown that from interferometric observations alone it is possible to find the angular diameter of the primary, the brightness ratio of the components of the binary, the angular size of the semi-major axis of the relative orbit, the eccentricity, the time of periastron passage, the longitude of the line of apsides, the inclination of the orbit, the position angle of the line of nodes, the period of the orbit and the sense of the orbital motion. For a Vir, spectroscopic observations give values for four of these parameters of higher accuracy than can be obtained from the present interferometric data. Therefore, in the final analysis, these parameters were fixed at their spectroscopic values. The results for the two series of observations are in good agreement and where a spectroscopic parameter could be determined independently from the interferometric observations the agreement with the spectroscopic value is good. Interferometric and spectroscopic results have been combined to obtain the distance of a Vir (84 j 4 pc) independent of interstellar extinction and luminosity criteria, the masses of the primary and secondary components, and the radius and surface gravity of the primary. The addition of photometric data has enabled the absolute emergent surface flux from the primary at I 83 -1 to be determined and, by comparing this surface flux with the predictions of theoretical model stellar atmospheres, the effective temperature of the primary has been estimated. Finally the luminosity of the primary and the absolute magnitudes of both components have been found.