Diatoms occur in almost all water reservoirs. Among the huge number of diatom species are those that occur almost everywhere, but there are also species specific to the environment. In addition, the diatom shell, which is the basis for their species differentiation, is resistant to most destructive factors. Thanks to the above features, diatoms can be an important determinant of diagnosing drowning as the cause of death. This publication uses protocols for forensic examination of corpses and diaconal protocols in internal organs drawn up in 2013–2017 at the Department of Forensic Medicine at the Medical University of Warsaw which is the only center in Poland that routinely performs the diatomaceous test. It has been shown that this test can be the main deter- minant of the cause of death in the case of examination of corpses included advanced late postmortem changesor and the lungs suffered extensive damage.