We present M3Depth, a self-supervised depth estimation method for laparoscopic imaging, leveraging 3D geometric consistency from stereo pairs while enabling monocular inference. By masking border regions and enhancing left-right overlap correspondences, M3Depth outperforms prior methods on public and newly acquired datasets, demonstrating strong generalization across samples and laparoscopes. Code and data are available at
https://github.com/br0202/M3Depth.