A handedness questionnaire consisting of thirteen items was administered to 4282 Japanese senior high school students. Information on the occurrence of left-handedness in their family as well as on forced conversion of hand usage in their childhood was obtained. Results indicated that incidence of non-right-handedness was 7.2%, with that of males being greater than that of females. The proportion of converted right-handers was greater in females than in males. When the frequency of converted right-handers was added to that of present non-right-handers, the average for non-right-handedness increased to 11%. Non-right-handers, particularly females, had familial sinistrality more frequently than right-handers. Item analysis revealed that the incidence of individuals who always use left hand for writing and eating was only 0.7% and 1.7%, respectively. This suggests that social pressure for right-hand writing and eating remains high in Japan.