The Pressure–Activation–Stress (PAS) scale is a self-report questionnaire for children concerning perceived stress. To explore behavioral and physiological correlates, we investigated if scores discriminate between a group prone to perceive high levels of stress [children with attention-deficit/hyperactivity disorder (ADHD)] and a healthy school sample, and if they are associated with diurnal cortisol levels. The PAS scale was filled in at home by children (11–17 years) with clinically confirmed ADHD (n = 102) and non-affected comparisons (n = 146). Saliva samples were collected four times during a regular school day for radioimmunoassay analysis of cortisol. Subtypes and severity of ADHD symptoms were determined using parental rating scales. Children with ADHD scored higher on the PAS scale than a school sample. The PAS scores were similar over ages in the ADHD group while they increased with age in the healthy group. Female sex was associated with higher stress in both groups but no gender interaction was found. No association was found between PAS scores and cortisol levels in neither group. Children in the ADHD group had a lower ratio of cortisol levels/perceived stress on all sampling occasions, built up both by the higher PAS scores and the lower cortisol levels in children with ADHD. The higher PAS scores in children with ADHD support the validity of the scale. The lack of association between PAS scores and diurnal cortisol levels is intriguing and illustrates the complexity of the stress concept. Stress-related fragility seems to accompany ADHD during childhood.