A new method is presented for automatic region detection of the maxillary sinus from human face X-ray radiographs. In this processing, firstly a new algorithm for transformation from continuous tone image to bi-level image using local properties of the image is introduced. Secondly, the region detection algorithm is introduced which is based on the considerations of the global shape informations of the maxillary sinus such as area, perimeter and complexity. As the results, it is shown that the regions of the maxillary sinus detected by computer are coincided well with the diagnosis by medical doctors.