The analysis of mammograms is a difficult task due to the subtle appearance of some lesions. Computer-aided diagnosis (CAD) have been shown to improve the sensitivity of detection of masses and calcifications; however, there is a need for dedicated methods to detect architectural distortion in the absence of a central mass. Improvement in the detection of architectural distortion may be expected to result in better prognosis for patients with early stages of breast cancer. By employing the concept of phase portraits, a method to characterize architectural distortion in mammograms using texture orientation fields is presented. The results obtained show that the proposed technique can achieve good discrimination between architectural distortion and other parenchymal patterns. Such a technique would be applicable, in a CAD system, to images that have cleared the stages of detection of calcifications and masses with no positive findings.