Three-dimensional organization of diaphragmatic lymphatics in five fetuses was studied by the lymphatic casts of scanning electron microscope. A new resin consisting of piperylene, acrylic ester and styrene was used instead of Mercox. The diaphragmatic lymphatics formed rich networks in the muscular portion. There were two layers of lymphatic networks, i.e. the submesothelial network and the deeper network and only one layer in the tendinous portion of the diaphragm. The lymphatic networks were more dense in the tendinous portion than these in the muscular portion. The lymphatics were mainly composed of main lymphatic vessels and anastomosing side branches. The side branches often communicated the submesothelial network with the deeper network in the muscular portion. The main lymphatics were connected at regular intervals by way of transverse side branches in the tendinous portion. Numerous constrictions and notches showing the presence of lymphatic valves were often found on the cast surface of the main lymphatic vessels and the side branches. The lymphatics extended as far as the terminal branches, i.e. the lymphatic lacunae recognized as broad, flattened and blind-ended. In the present study, three-dimensional organization of human diaphragmatic lymphatics was for the first time described. It was suggested that the passageway of the lymph flow out of the peritoneal cavity may be explained. From the peritoneal stomata, the lymph of the peritoneal cavity flowed into the channels under the peritoneum, then into the lymphatic lacunae and finally into the lymphatic networks under the diaphragmatic pleura.