Purpose: To evaluate the mammographic findings of the sternalis muscle and discuss appropriate approaching. Materials and Methods: Ten years records of our mammography unit were retrospectively looked for sternalis muscle presence. This variant was seen in 10 of 52930 women. The mammograms of these patients were re-evaluated. The size, shape and contours of the muscle were reviewed on craniocaudal (CC) and mediolateral oblique (MLO) views. Yearly mammograms were assessed to evaluate the follow-up changes. Extra examinations such as ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) were reviewed. Results: The sternalis muscle prevalence was 0.018 %. Its contours were well-defined, irregular or spiculated and the diameter ranged from 3-4 mm to 15 mm. Its shape changed from slightly bulging to round or triangular. The muscle was detected on MLO projections in three patients as an inferiorly lying soft tissue density in the posterior edge of the breast, continuing with the pectoralis muscle. Distinct pulling of the breast led to variances on yearly mammograms. US examinations were normal in all patients. CT and MRI showed the muscle clearly. Conclusion: The sternalis muscle may have varying appearances on CC views. It may also be detected on MLO projections. Its appearance depends on good positioning. Knowledge of its detectability on mammograms prevents misdiagnosis of mass and concurrently proper approach prevents further investigations.