Answers to the question just what is the ‘case’ partly defined the fields of sociology and social work in early 20th century Chicago. Drawing on the archives of the University of Chicago, I describe and appraise the way the ‘case’ figured in social work at Chicago and elsewhere. I ask the corresponding question of sociology. Finally, I briefly consider why not much came of social work and sociology ploughing similar territory in ways that served for a time to hallmark their identities. This analysis opens up ways of rethinking how social work and sociological research are distinctive to their fields, and allows a less ‘pre-tuned’ discussion of how practitioners of either might reciprocally pursue their profession.