One hundred twenty-eight children in preschool through fifth grade (range= 4,3–1,4) and 76 adults serving as a comparison group participated in two studies that examined how children reason about psychogenic bodily reactions, that is, ailments or nonconscious physiological responses with origins in the mind (e.g., stress-induced headache). Psychogenic bodily reactions provide an opportunity to study how children integrate knowledge between the domains of bodily response and psychology. In Study 1, participants were asked whether various familiar psychogenic bodily reactions were possible (e.g., can someone get a tummyache from worrying?). In Study 2, participants were presented with a novel domain (hypothetical “aliens” from outer space) and were asked whether various unfamiliar bodily conditions (e.g., toes swelling) could arise from various physical or psychological causes. As predicted, adults typically reported that psychogenic bodily reactions were possible, and that unfamiliar bodily conditions could result from either psychological or physical causes. In contrast, young children typically denied that psychogenic bodily reactions could occur and predicted that unfamiliar bodily conditions resulted from physical causes only. The results support a developmental path: younger children view psychogenic bodily responses as wholly physical, but with age, view them as both physical and psychological phenomena.