EN
Execution of dedicated business software systems Development and Enhancement Projects (D&EP) encounters many problems, leading to the high scale of their failure, what has its effect in considerable financial losses. Such problems first of all include: conscious lowering of the D&EP costs to win a contract, the functional requirements increase without taking it into account in the D&EP costs as well as unrational clients commitments ex ante and ex post establishing. The reduction of such problems can be caused by so-called functional assessment of D&EP, that is the assessment based on their products functional size measurement. This paper is aimed at synthetic presentation of own D&EP functional assessment concept, including its assumptions, aims, stages and criteria.