Seventy-five patients aged 7 to 17 with juvenile chronic arthritis were interviewed to identify their beliefs about the physical nature of their illness and the relevance and modes of action of their clinical treatment. Children in the 7-11 age group were found to perceive their arthritis largely in terms of its immediately manifestations, to have little conception of internal pathology, and to be less aware of the value of their medical therapy. Children in the 12-17 age group showed a greater tendency to recognize arthritis as a condition of internal pathology, to experience distressing fantasies about the internal appearance of their affected joints, and to appreciate the purpose of their therapy.