Isabel Menzies Lyth’s landmark account of a nursing service, “A Case Study in the Functioning of Social Systems as a Defence against Anxiety” (1960), is well known, and it contains a fundamental truth that seems to elicit instant recognition from every kind of reader. In revisiting this paper for a colloquium on social defences, I became aware of several aspects of the paper that I had not previously noticed. Although she describes the social defence as a protection for nurses against the impact of the nursing task, the stress and anxiety that it created in them was far from protective. Furthermore, although the paper refers to primitive anxiety in general, it never actually names the specific anxiety nor the specific defence that is embodied in the care system. The data are provided but not the conclusion. Would it be possible, I wondered, to take this missing step now? With this question in mind I re-read the ten sections that describe the nursing techniques, and I was struck by the use of language associated with obsessional mechanisms. Was the social defence that Menzies Lyth had in mind—but did not name—one of obsessionality? If it was, then perhaps naming the defence would also disclose the unnamed anxiety. The first question is: how far does her description of the social defence correlate with obsessional mechanisms? Answering this question will involve recapitulating some familiar territory.