PICOS was a three-year population-based study in the Veneto region, focusing on first-episode psychosis (FEP) patients in public mental health services. It involved 25 collaborating sites with a naturalistic longitudinal design, covering clinical, social, genetic, and brain imaging aspects. The study recruited individuals aged between 15 and 54 who exhibited specific psychopathological symptoms for the first time, excluding those with prior long-term antipsychotic treatment or mental disorders due to medical conditions or severe mental retardation. All participants displayed at least two of the following symptoms: loss of interest, initiative and drive, social withdrawal, episodic severe excitement, purposeless destructiveness, overwhelming fear, or marked self-neglect. Evaluations of both patients and relatives were carried out at baseline and at 1, 2 and 5 years.