Hospitalization of a child in the paediatric intensive care unit (PICU) is extremely stressful, both for the child and for his or her family. The purpose of this study was to gain deeper insight into the stressful experiences of parents of children hospitalized in the PICU. This study included 96 parents. The data were collected using a translated and standardized scale “The Parental Stressor Scale: Paediatric Intensive Care Unit (PSS: PICU)”. This study confirms high exposure of parents to numerous PICU stressors. The most intense PICU stressor for parents was child’s breathing depending on the ventilator (4.22 ± 1.17), and the least intense was child’s demanding behaviour (1.17 ± 0.33). A significant positive correlation between the level of parents’ perceived stress and the number of their children was recorded (r = 0.240, p = 0.02), while there was no significant correlation between the level of stress and other sociodemographic variables. A significantly higher level of stress was experienced by parents with primary school education (p = 0.032) and parents who are not healthcare professionals (p < 0.01). It is necessary to establish a system that will enable continuous assessment of parents’ stress levels and timely prevention of stressful experiences for parents in the PICU.