Abstract
The majority of writers publishingin the legalliterature agree that a testament (lastwill) is a specific, unilateral and retractable legalact or simply a unilateral and retractable statementof will which comes into effect upon the deathof the testator. According to Polish civil law,art. 945 par. 1 of the civil code, a testament is invalidif it was produced (1) in a condition precludinginformed or free decision and expression of will, (2) as a result of a misconception justifyingthe suspicion that, had he/she not acted under theinfluence of this misconception, the testator wouldnot have produced a testament of such content,(3) in response to threat. If the testator is deadand members of the family go to court seeking invalidationof the will on the grounds of one of thesecircumstances, the court appoints one or more forensicpsychiatrists and psychologists and requeststheir expert opinion. Generally speaking, the psychologist'stask is to reconstruct the testator'sstate of mind when producing the will so that thecourt may, on the basis thereof, refute or confirmthe suitor's objections. A methodological model of the psychologist's ex post facto diagnostic proceedingsis presented. The psychologists draws his data from the court documentation (witnesses' evidence,significant medical documentation etc.) and, ifnecessary, he also interviews significant persons(on the court's permission).