A combined toilet and waste holding tank is provided for mounting within a portable toilet cabana having side walls, a rear wall, and a front wall with a door and a floor. The tank extends along the rear wall and between the side walls and occupies roughly the rear half of the cabana floor space. The toilet includes a ring-like structure having a rear portion opening directly into the tank through a cover panel upon the upper surface of the tank, and also having a forward extending, bowl-like portion which is integral with and extends forwardly of the front wall of the tank. The cabana has a rear-to-front extending central axis which approximately bisects the cabana. The toilet structure is located substantially on one side of the cabana axis, so that it is closer to one side wall of the cabana and the toilet is acutely angled relative to the cabana axis. The front wall of the tank is angled relative to the cabana axis so that it is perpendicular to the axis of the toilet on opposite sides of the toilet bowl-like portion. The arrangement provides increased occupant usable floor space within the cabana, enables nesting a pair of tanks for storage and shipment independently of the cabana, and functions as both a urinal and toilet.