This paper considers insights for contemporary medical practice from an archival study of gratitude in letters exchanged between almoners at London's Brompton Hospital and patients treated at the Hospital's tuberculosis sanatorium in Frimley. In the era before the National Health Service, almoners were responsible for assessing the entitlement of patients to charitable treatment, but they also took on responsibility for aftercare and advising patients on all aspects of welfare. In addition, a major part of the work of almoners at the Brompton was to record the health and employment status of former sanatorium patients for medical research. Of over 6000 patients treated between 1905 and 1963 that were tracked for the purposes of Medical Research Council cohort studies, fewer than 6% were recorded as 'lost to follow-up'-a remarkable testimony to the success of the almoners' strategies for maintaining long-term patient engagement. A longitudinal narrative case study is presented with illustrative examples of types of gratitude extracted from a corpus of over 1500 correspondents' letters. Patients sent money, gifts and stamps in gratitude for treatment received and for the almoners' ongoing interest in their welfare. Textual analysis of letters from the almoner shows the semantic strategies that position gratitude as central to the personalisation of an institutional relationship. The Brompton letters are conceptualised as a Maussian gift-exchange ritual, in which communal ties are created, consolidated and extended through the performance of gratitude. This study implicates gratitude as central to the willingness of former patients to continue to engage with the Hospital, sometimes for decades after treatment. Suggestions are offered for how contemporary relational healthcare might be informed by this unique collection of patients' and almoners' voices.