This paper suggests that the practice of anamnesis—the taking of a patient history in preparation for making a diagnosis, as well as the related form of investigation, historia—offers a way to understand the role of medical collections in generating medical knowledge. Anamnesis derives from ancient Greek “recollecting” or “opening of memory,” and “taking a history” from historia, an ancient and early modern epistemic practice of gathering empirical observations from the past and present. Doctors and medical researchers perform, this paper argues, a form of anamnesis when they access collections—of pathological organs, experimental animals, diagnostic slides, samples, and data—and the collections may in turn be seen as constituting institutional and disciplinary memories. It moreover shows that doctors and medical researchers in their work with collections negotiate two ways of organizing observations that are also present in an anamnesis. One way clusters and classifies observations, while the other traces developments and requires significant past observations to understand the present. This double nature plays out in different ways in different historical collections. Last, the paper itself may also be seen as performing an anamnesis: looking for patterns and tracing a development in medical history. It “opens the memory” of medical collection practices, and shows that medicine is past-heavy and that the past plays a central role in modern biomedicine. Anamnesis is thus used as a historiographical stance that seeks to understand present practices of generating knowledge about diseases through an inquiry into the past.