Introduction: Patients’ perception of an intensive care unit (ICU) stay can lead to a better understanding of the expectations and needs of patients hospitalized in intensive care so that care for critically ill patients can be adapted and improved. Thank you letters are sources of original information which come directly and spontaneously from patients. Objective: The objective of this study was to analyse the thank you letters from patients who required intensive care treatment and to identify messages that could be intended for the ICU team. Design: We conducted a qualitative study according to a thematic analysis. The body of research consisted of 17 letters from patients hospitalized in ICU. Setting: The study took place in the medical-surgical ICU of a French general hospital. The ICU is made up of 16 resuscitation beds and 4 beds of continuous monitoring unit. Findings: Two main themes emerged: (i) expression of gratitude through a description of the caregivers’ behavior (humanity and professionalism) and recognition for surviving (ii) the narrative of the ICU experience. Conclusion: Thank you letters give a rich insight into how the patients perceived their stay in ICU. Letters from patients give direct feedback on the quality of care provided, contribute to give meaning to work and raise the question of what the core values of care should be for all concerned in the healthcare providers-patients relationship.