Brain diseases and psychiatric conditions have an annual economic impact in the trillions globally, with dramatic increases projected over the next several decades. Yet some of the most widespread, severe, and disabling conditions are defined by clinical criteria developed long before the recent advancements in genetic testing and personalized medicine. Dated approaches may result in delayed or inaccurate diagnoses, which lead to ineffective treatment. Further, because the presentation and severity of symptoms can depend on multiple factors, including concurrent conditions and biological background, one-size-fits-all remedies to most neurological conditions are unlikely to benefit most patients. A new approach is needed to move beyond basic diagnostic labels and harness the power of big data to build better, biologically informed diagnostic definitions and treatments. How close is this future in psychiatric and neurological care?