Aim: To test that age is of influence on midazolam requirements during prolonged mechanical ventilation in critically ill children. Methods: Retrospective observational study of children (28 days-18 year) admitted between January 1st 2002 and January 1st 2005 who needed controlled mechanical ventilation for 5 days and initial sedation with midazolam were included. Exclusion criteria were psychomotor retardation, therapeutic use of midazolam, ventilator weaning within 5 days, kidney or liver failure. Results: A total of 1186 children were admitted, of which 58 children were included. The children were divided into three age groups: 28 days-1 year (n = 28), 1-4 years (n = 16) and older than 4 years (n = 14). Within 2 days the children age 1-4 years received the maximum midazolam dosage (0.3 mg/kg/h). In addition, the mean total dose of midazolam was higher at all days for this age group. At day 5 none of the children between 1 and 4 years could be sedated with midazolam alone. Conclusions: Our data showed that children between 1 and 4 years needed higher doses of midazolam as compared to children who were younger and older. Furthermore, we observed that midazolam alone is a poor sedative for all age groups. The influence of and mechanisms for possible age related effects on midazolam requirements remain to be elucidated, as well as the position of midazolam as a first line drug for PICU sedation. © 2007 The Author(s).