We derive the parameters of the hot, massive close binary system UU Cas from earlier and recent photoelectric UBV R observations: M-1 = 34.5M(circle dot), M-2 = 25.7 M-circle dot, A = 69R(circle dot), and i = 68degrees; the components' limb darkening coefficients are close to 1. Our fitting of the light curves provides evidence for a high degree of over-contact: the components fill their inner critical surfaces by 132% and 100%. It is possible that the appearance of the light curve is determined not only by the distorted shapes of the components and their eclipses but, to a considerable extent, by screening by a complex envelope and the envelope's contribution to the system's total luminosity. (C) 2002 MAIK "Nauka/Interperiodica".