The PESSOAS surey collected data in order to assess behaviors and estimate HIV, syphilis, hepatitis B, hepatitis C seroprevalence in persons with chronic mental illness. Along with that, the survey investigated sociodemographic characteristics of the patients and the environments of the facilities. The randomly selected participants of the study were age 18 years and over, and either hospitalized in a psychiatric facility or receiving care in facilities known as Psychosocial Care Centers (CAPS).
 
Data was collected through interviews with patients at facilities, interviews with staff at facilities, medical records, and blood samples. The data collection took place from June through October of 2006. The patient interviews focused on collecting sociodemographic and behavioral information. The blood samples were used for serological tests for HIV, Hepatitis B, Hepatitis C, and syphilis. A total of 2,475 participants were interviewed and of those, 2,238 also had blood samples taken.