Clinicians across medical disciplines are intimately familiar with an unusual feature of descriptive diagnoses. The diagnostic terms, despite their non-aetiological nature, seem to offer an explanatory lens to many patients, at times with profound effects. These experiences highlight a striking, neglected and unchristened medical phenomenon: the therapeutic effect of a clinical diagnosis, independent of any other intervention, where clinical diagnosis refers to situating the person’s experiences into a clinical category by either a clinician or the patient. We call this the Rumpelstiltskin effect. This article describes this phenomenon and highlights its importance as a topic of empirical investigation.