Currently, most elective pediatric surgery is performed on an out-patient basis. The objective of this case-control study was to identify potential determinants of patient cancellation at a children's hospital. Cases were defined as patients that were canceled on the day of surgery, whereas controls were those patients who underwent surgery on the scheduled date. Demographic and clinical data were collected using chart review. Approximately 10% of all day surgery patients were canceled on the day scheduled for surgery, half for reasons deemed preventable. Of the preventable cancellations, stepwise logistic regression analysis showed that patients attending only the surgeon's office prior to day surgery, were more likely to be canceled because of inadequate preparation, compared to those patients attending both the surgeon's office and the hospital preoperative clinic (adjusted odds ratio = 3.18; 95% CI: 1.32, 7.63).