Objectives: Previous research in adult patients with blunt hepatic injuries has suggested a pattern of serum hepatic transaminase concentration decline. Evaluating this decline after pediatric blunt hepatic trauma could establish parameters for estimating the time of inflicted injuries. Deviation from a consistent transaminase resolution pattern could indicate a developing complication. Methods: Retrospective review of pediatric patients with injuries including blunt liver trauma admitted to one of four urban level 1 trauma centers from 1990 to 2000. Cases were excluded for shock, death within 48 h, complications, or inability to determine injury time. Transaminase concentration decline was modeled by individual patients, by injury grade, and as a ratio with regard to injury time. Results: One hundred and seventy-six patients met inclusion criteria. The rate of aspartate aminotransferase (AST) clearance changed significantly over time. Alanine aminotransferase (ALT) fell more slowly. Of the 118 patients who had multiple measurements of AST, for 112 (95%) the first concentration obtained was the highest. When ALT was greater than AST, the injury was older than 12h (97% specificity (95% CI, 95-99%), sensitivity 42% (95% CI, 33-50%)). Patients with enzymes that rose after 14 h post-injury were more likely to develop complications (RR = 24, 95% CI 10-58). Conclusions: Hepatic transaminases rise rapidly after uncomplicated blunt liver injury, then fall predictably. Persistently stable or increasing concentrations may indicate complications. ALT greater than AST indicates subacute injury. (Contains 3 figures and 4 tables.)