When a robot moves about a 2D world such as a planar surface, it is important that obstacles to the robot's motions be detected. This classical problem of "obstacle detection" has proven to be difficult. Many researchers have formulated this problem as being the process of determining where a robot cannot move due to the presence of obstacles. An alternative approach presented here is to determine where an robot can go by identifying floor regions for which the planar floor assumption can be verified. A stereo vision system is developed for Floor Anomaly Detection (FAD), and its relationship to existing stereo obstacle detection algorithms is described.