As a general problem in nosology, the moment when one becomes ill may be hard to define. In Psychiatry, the boundaries of disease may be more difficult to establish. In the last decade, we’ve been observing a growing interest in early diagnosis in this field, and the concept of “transition” to a mental illness became an important topic of discussion with implications in clinical practice.

To review different author's models of evolution of symptoms and transition to mental illness and discuss their advantages and limitations in the actual context of Psychiatry research and clinical practice.

To increase understanding on the different paradigms of becoming ill and their relevance to present and future psychiatric practice.

Non-systematic review of literature devoted to the creation of models that describe the establishment of a mental disorder.

One of the first accounts of becoming mentally ill was developed by K. Jaspers within a phenomenological life-history analysis. Nonetheless, a cross-sectional approach to diagnosis has dominated Psychiatry for most of the time. With the advent of early intervention studies, longitudinal models of disease have been emphasized. The concept of a transition to disease was then operationalized but also highly criticized. Recently, McGorry proposed a staging model for psychiatric disorders in continuum with the non-clinical population. Finally, a dynamic systems approach to diagnosis in Psychiatry will be discussed.

Driven by research in early phases of mental illnesses, current models of disease propose a longitudinal approach that emphasizes the complex and non-linear course of symptom clusters.

The authors have not supplied their declaration of competing interest.