In medicolegal practice, rare cases involving suicidal, criminal, or accidental insulin overdose are both analytically and forensically challenging. The aim of this study is to present a model procedure in such cases, developed at the Department of Forensic Medicine and Toxicology of the Medical University of Silesia in Katowice, with particular emphasis on the possibility of additional confirmation of insulin intake by its immunohistochemical detection at the injection site. In the example case presented here, an immunohistochemical examination using FLEX Polyclonal Guinea Pig Anti-Insulin antibody (code IR002, Dako) confirmed the presence of insulin in the subcutaneous tissue of the victims. In our opinion, the method of immunohistochemical detection of insulin at the injection site can and should be used routinely in such cases.