PURPOSE: Paracetamol has been associated with a reduction in blood pressure, especially in febrile, critically-ill adults. We hypothesised that blood pressure would fall following administration of paracetamol in critically-ill children and this effect would be greater during fever and among children with a high body surface area to weight ratio. METHODS: A 12-month prospective observational study of children (0-16years) admitted to paediatric intensive care, who underwent pulse contour analysis and received paracetamol concurrently. RESULTS: Mean arterial blood pressure decreased significantly by 4.7% from baseline (95% CI 1.75-8.07%) in 31 children following 148 doses of paracetamol. The nadir was 2-hour post-dose. The effect was pronounced in children with fever at baseline (6.4%, 95% CI 2.8-10%), although this was not statistically significant. There was no simple relationship between this effect and body surface area to weight ratio. The association between a change in blood pressure and changes in heart rate or measured stroke volume was poor; therefore it was likely that a change in the systemic vascular resistance contributes most to this effect. CONCLUSION: There is a significant but modest reduction in blood pressure post-paracetamol in critically-ill children. This is likely related to a change in systemic vascular resistance.