Although stress assessment is important in different health areas, there are few instruments with adequate psychometric evidence to assess it. The study aimed to present new validity evidence of Lipp’s Inventory of Stress Symptoms for Adults (LSSI), describe and discuss clinical characteristics of the LSSI with data obtained from patients seen in a hospital outpatient clinic and a Psychosocial Care Center (Centro de Atenção Psicossocial - CAPS). Sampling was based on post-stratification via the Raking method. In total, 4,500 participants from all over Brazil of both sexes, different age groups and academic levels composed the study. The results via Item Response Theory indicated a structure with high internal consistency. Symptoms of apathy, depression or prolonged anger were the most associated with stress and women scored higher. There was a significant correlation between the LSSI-R and another mental health measure (DASS-21) in the clinical group.