Segmentation of the Region of Interest (ROI) is the first and crucial step in the analysis of digital mammogram images since the success of any Computer Aided Diagnostic (CADx) system depends greatly on the accuracy of the segmentation of the ROI from the mammogram images. Finding an accurate, robust and efficient ROI segmentation technique still remains a challenging problem in digital mammography analysis. In this paper we have proposed an efficient Otsu's N thresholding method for segmenting regions of interest from the mammogram images. Digital Mammograms are taken from the mini MIAS(Mammographic Image Analysis Society) database for the purpose of experimentation and the results obtained are scaled to full color. Results show that the proposed method is efficient and is in concurrence with the ground truth table available in the database.