Critical illness and intensive care therapy are often followed by psychological problems such as nightmares, hallucinations, delusions, anxiety, depression, and symptoms of posttraumatic stress. Intensive care patient diaries have been kept by nurses and the patients' family since the early 1990s in the Scandinavian countries to help critically ill patients come to terms with their illness after hospital discharge. The aim of the study was to describe and compare the emergence and evolution of intensive care patient diaries in Denmark, Norway, and Sweden. The study had a comparative international design using secondary analysis of qualitative data generated by key-informant telephone interviews with intensive care nurses (n=114). The study showed that diaries were introduced concurrently in the three Scandinavian countries as a grass-roots initiative by mutual cross-national inspiration. The concept has evolved from a pragmatic practice to an evidence-based domain of inquiry propelled by academically prepared nurses. Several schools of thought were identified in our study: diaries as (i) a therapeutic instrument, (ii) an act of caring, (iii) an expression of empathy, and (iv) a hybrid of the above. Diaries have the potential to fulfill the existential needs of patients who struggle to make sense of their experiences and construct their own illness narrative.