This paper focuses on the role and importance of psychological diagnosis andragogic in achieving educational outcomes are studying the system of additional vocational training. The article presents the author's view on the nature and content of the diagnostic features of adult learners embarking on additional professional development programs. Analysis of the results of research by leading scientists on adult education and their own practical experience of the author in the system of additional vocational education led to conclusions about the need to identify the input stage to diagnose educational facilities and the needs of students, the existing level of their professional and social competence, identify barriers to learning. Emphasizes the importance of the selected diagnostic components in the organization focused adult socialization by means of additional professional education.