To begin with it will be necessary to note that it is not my intention in this paper to give a complete account of the — more or less important — sources of error in the tables of invalidity which at present usually are employed by the Danish companies in the private pension assurance business. On the contrary I intend only to examine the consequences of a few of the errors which one cannot avoid noticing when regarding the methods of constructing the tables, or which — in my opinion — are of very great importance for the definite results.