A standard model of analytical preoperative profile does not exist, so we decided to perform a wide profile. In this revision, we studied the utility of determining serum ALT activity in analytical preoperative controls, searching for the causes of its elevation in pediatric patients who would undergo minor surgery. Of the 3,750 patients analysed, 1.57% showed elevated serum ALT activity. Searching for the main cause, we found the following groups: I) patients with diseases unrelated to the surgical procedures that cause elevated serum activity; II) patients on pharmacological treatments which may produce transitory elevations of serum ALT activity, and III) patients with elevated serum ALT activity that has no evident clinical or pharmacological cause. The high incidence of patients with this abnormality justified the inclusion of serum ALT activity in the profile. We conclude that: a) the reasons for this elevation should be investigated, b) pediatricians should consider postponing surgery, and c) resumption of normal serum ALT activity should be monitored.