BACKGROUND: While American Society of Anesthesiologists and European Society of Anaesthesiology guidelines recommend 6 h pre-anaesthetic fasting for food and non-clear fluids in children, some institutions allow shorter fasting times of 4 h. Aim of this pilot study was to compare weight-indexed residual gastric contents volumes (GCV(w) ) after 4 vs. 6 h after a light breakfast, using magnetic resonance imaging (MRI) in healthy volunteer children not scheduled for anaesthesia. METHODS: Four vs. 6 h (F(4) /F(6) ) of food fasting were simulated in a crossover study. After overnight fasting (baseline), each child ingested a light breakfast (cereal flakes, milk products) on two separate days. Additional clear fluid (7 ml/kg raspberry syrup) was given either after 2 (F(4) ) or 4 h (F(6) ), followed by half-hourly MRI acquisition for 2 h. MRI was obtained on a 1.5 Tesla scanner as 5 mm axial images (FIESTA) and volumes were traced manually by one blinded observer. Data are given as median (range) or mean ± standard deviation. RESULTS: Eighteen healthy volunteers aged 9.0 (6.8-12.2) years participated. GCV(w) for F(4) and F(6) at baseline was 0.50 ± 0.27 and 0.76 ± 0.48 ml/kg (P = 0.07), respectively, GCV(w) after 4 and 6 h was 0.72 ± 0.85 and 0.47 ± 0.25 ml/kg (P = 0.88). T(1/2) after syrup intake was 30.8 ± 12.2 and 28.3 ± 5.7 min (P = 0.47) for F(4) and F(6) , respectively. CONCLUSION: Residual gastric contents volumes at a hypothetical anaesthesia start were similar for 4 and 6 h food fasting in healthy volunteer school-age children.