Thirty surgery patients between 4 and 12 years of age were interviewed preoperatively to assess their knowledge about medical instruments (e.g. the indentity and function of an anesthesia mask). Self-report measures of anxiety were also obtained Qualitative and quantitative age differences in children's understanding of medical instruments were noted, but no age differences were detected in overall level of anxiety of in the rank ordering of items considered least and most anxiety provoking Children who were most anxiety appeared to have the least understanding of medical instruments. These findings are discussed in terms of the literature on providing children with medical information. Recommendations for preparing different-aged children for medical procedures are offered.