Background: Use of dexmedetomidine in critically ill pediatric patients is increasing despite limited data on effects on mechanical ventilation times, use of other sedatives, adverse effects, and withdrawal. Objectives: To describe the use and tolerability of dexmedetomidine in a large cohort of critically ill children. Methods: This was a retrospective cohort study of patients receiving dexmedetomidine in a pediatric intensive care unit. Ethical approval was granted by the local review board. Data on dexmedetomidine administration, ventilatory support, other sedatives, adverse effects, and withdrawal were collected. Results: There were 219 patients included. Dexmedetomidine was a first-line sedative in 47.9% of patients; the median infusion duration was 27 hours. Of patients on other sedatives at dexmedetomidine initiation, 39.5% had a dose reduction in those sedatives by 24 hours. Use of dexmedetomidine in noninvasively ventilated patients was common (19.6%), as was use in patients on no ventilatory support (35.6%). Patients receiving no ventilatory support used dexmedetomidine for shorter durations (P = 0.001) and were less likely to have received prior sedatives (P < 0.001). Adverse effects occurred in 42% of patients and were associated with younger age (P = 0.001) and longer dexmedetomidine duration (P < 0.001). The majority of patients (65%) were weaned off dexmedetomidine, and 80% of patients had at least one sign of withdrawal. Conclusions: Our data suggest substantial use in noninvasively ventilated patients. Adverse effects appeared more common in younger patients and those with prolonged infusions. A high rate of withdrawal effects was seen; no associations with age, dose, or duration were found.