There are numerous ways in which human beings respond to humour: they smile, grin, laugh, giggle or guffaw, and their behaviour might include anything from a glint in the eye to an uncontrollable heaving of the whole body. We consider how laughter is displayed in the lives of four children with profound and multiple learning difficulties and disabilities (PMLD), and reflect on what this reveals about their capabilities and relationships. We introduce three theories of humour - as expressions of superiority or relief, and as prompted by a sense of incongruity - and we explore how teachers and actors incorporate absurdity and incongruity in their work with children with PMLD. We suggest that laughter can both serve to reveal complex cognitive and affective capabilities and function so as to enable children with PMLD to develop relationships and to be seen as fully our fellow human beings.