Objective: To discuss potential advances in neuroscientific knowledge in the 21 st century, enabling the realization of Freud's original vision of a basic biological science and an associated metapsychology. Results: The Australian Twin Study of Attention Deficit Hyperactivity Disorder (ADHD) has demonstrated the high heritability of the core symptoms of ADHD, as well as showing important genetic and environmental influences on comorbid conditions. Brain mapping techniques suggest that working memory, as measured by an A-X Continuous Performance Task, is important in ADHD. Methods: To outline the development of our own clinical research into ADHD, and the potential for future behaviour and molecular genetic approaches. Conclusions: The 21st century promises new and exciting developments in phenomenology, genetics, and neuroscientific understandings in Child Psychiatry.