The detection of small quantities of unsuspected free intraperitoneal fluid (IPF) at US examination in children has increased markedly in our department since linear high-frequency probes have been used routinely for gastrointestinal examinations. Its clinical significance is unknown. OBJECTIVE. This study attempted to evaluate the sonographic detection, quantification and location of IPF in an unselected paediatric population using both convex or sector scan heads and a linear US probe in all to compare the results obtained using different probes.