Objectives: to compare intermittent mandatory ventilation (IMV) with synchronous intermittent mandatory ventilation associated with pressure support (SIMV/PS) related to duration of mechanical ventilation/weaning and length of stay in PICU (LS). Design: randomized clinical trial. Setting: Pediatric intensive care unit at a university-affiliated hospital. Patients: children between 28 days and 4 years old, admitted between 10/2002 and 06/2004, and receiving mechanical ventilation (MV) for more than 48 hours. Patients were randomly assigned into two groups: IMV (IMVG; n=35) and SIMV/PS (SIMVG; n=35). Children with acute respiratory distress syndrome and tracheostomy were excluded. Ventilation and oxygenation data were recorded at admission and beginning of weaning. Results: Groups were not statistically different for age, gender, MV indications, PRISM score, COMFORT scale, sedatives, and ventilation and oxygenation parameters. Median of MV duration was 5 days for both groups (p>0.05). Also, there were no statistical differences for duration of weaning [IMVG: 1 day (1 - 6) vs. SIMVG: 1 day (1 - 6); p>0.05] and LS [IMVG: 8 days (2 - 22) vs. SIMVG: 6 days (3 - 20); p>0.05]. Conclusion: There was no statistically significant difference between IMV and SIMV/PS in these children related to MV and weaning duration, and PICU length of stay.