We often have a feeling that we know ourselves much better than others know us, coupled with a feeling that our minds are not transparent to other people. In this article we begin to explore cultural variations in the development of this feeling. Children in Britain and Japan aged 7, 9 and 11 years judged how well they and how well their parent/teacher knew about aspects of the child's mind (e.g., dreams, feeling sick, feeling hungry). Compared with British children, Japanese children credited adults with relatively large amounts of knowledge about themselves and this was most notable in the youngest group. Differences in patterns of judgements between the two nations could arise from differences in the cultural influences on the rate of development.