We present new full-orbit spectroscopic and I(Kron)ybvu photometric observations of the totally eclipsing long-period Algol-type binary DN Orionis. We carry out new radial velocity and light solutions, which include the rapid rotation of the hotter star. We show that the cool component does not quite fill its Roche lobe, though an accretion disk is present around the hotter star (as shown by double-peaked Ha emission and excess O I λ7774 absorption). Simple Roche-lobe overflow therefore cannot explain this circumstellar matter. Absolute system parameters are obtained from the cool-star radial velocity amplitude and a fairly well determined photometric mass ratio. During primary eclipse totality, we find about 0.3 mag of excess ultraviolet emission radiated by the uneclipsed outer edges of this disk. DN Ori joins several other long-period Algols with a slightly detached configuration, a supersynchronously rotating hot star, and a low-mass evolved cool star.