Japanese national sentiment has been described as paternalistic, which has potentially wide-ranging implications for the manner in which psychiatric patients should participate in medical decision-making. To examine the extent and possible determinants of the desire to participate in medical decision-making among Japanese people, we distributed a packet of questionnaires to 747 (nonmedical) university students and 114 of their parents. The questionnaires included an imaginary case vignette of psychotic depression. The participants were asked whether they would want various types of medical information, i.e., diagnosis, aetiology, treatment, outcomes, medical charts, etc., disclosed to them were they in such a psychiatric condition. Also included was the 1995 Scale for Independent and Interdependent Construal of the Self by Kiuchi. More than half of the participants wanted all the types of medical information disclosed to them. Those participants who wanted to have all types of information disclosed to them (n = 413) as compared to those who did not want to know at least one type of information (n = 445), tended to be male and to have an educational background in psychiatry (9.7% vs 5.4%) as well as an assertive attitude as indicated by a higher score on Independence on the Scale for Independence and Interdependent Construal of the Self. These results suggest that the Japanese in this sample are more likely to want to make an autonomous contribution to the psychiatric decision-making process and that less desire for information can be predicted by some demographic and personality factors.