The author tries to define the adulthood. After reviewing the available definitions he has paid attention to the new phenomenon of 'postponing the adulthood'. Searching for the definition the author asked his students to define maturity and can distinguish three categories of their answers: adulthood concerning myself, adulthood concerning myself and others, adulthood concerning myself, others and the society. What is more, the students stress the value of individual experience as a developmental factor. The adulthood is therefore difficult to define. In author's opinion the adulthood is revealed in the situations , in which we make appropriate choices, act rationally and solve our problems.