Fears are very common during childhood. While some decrease as children grow up, others increase with age. They are usually more prevalent in girls than in boys and many seem to have an evolutionary meaning. Although there have been numerous studies about specific fears in children, there are few studies focused on social fears, particularly social situations provoking social anxiety/uneasiness. There is a lack of self-report instruments for assessing this problem. The present study shows the development and application of a new self-report instrument for assessing social anxiety children, the Social Interaction Questionnaire for Children (CISO-N). The measure consists of 82 items typically found in childhood. The instrument was applied individually to boys and girls from 9 to 12 years of age. Later on, several statistical tests were performed such as exploratory factorial analysis and concurrent validation with the Fear Survey Schedule for Children-Revised (FSSC-R; Ollendick, 1983). Six factors were found to explain 40% of the variance and included 64 of the 82 items of the questionnaire. Females scored significantly higher than males in all the factors, but within same gender there were few differences associated to age. Results are discussed and guidelines for future research are suggested.