Maintenance of the patient-ventilator system is the primary role of the respiratory care practitioner in the intensive care unit. Patient-ventilator system checks should include monitoring the patient's response to ventilation, evaluating function of the ventilator, maintaining ventilator settings according to physician orders, setting appropriate alarms, maintaining the integrity of the ventilator circuit and humidifier, and documenting all of the above. The concept of ventilator checks should be expanded and thus, the name changed to patient-ventilator system check to emphasize the importance of evaluating the patient. This article reviews the rationale for performing patient-ventilator system checks and measurements.