OBJECTIVE This study established the incidence and primary causes of unplanned extubation in newborns in the neonatal intensive care units of the Hospital Sofia Feldman, Belo Horizonte (Minas Gerais). METHODS This retrospective study was conducted between July 1, 2009 and April 30, 2010. Unplanned extubations and their primary causes were assessed using an adverse events form. The following variables were assessed: gender, corrected age, present weight, duration of mechanical ventilation time, and motives/causes of the event on the day of the unplanned extubation event. RESULTS Fifty-four unplanned extubations occurred, which corresponded to an incidence of 1.0 event/100 days of mechanical ventilation. This rate was higher among newborns with a corrected age of 30 to 36 weeks and weight < 1,000 g. The primary causes of unplanned extubations included patient agitation, inappropriate handling of patients during the performance of procedures, and inappropriate fixation and positioning of the endotracheal tube. CONCLUSIONS The incidence of unplanned extubation in the investigated neonatal intensive care units was low during the study period compared to previously reported data. Nevertheless, the assessment of the quality of procedures, the continuous follow-up of newborns, and the monitoring of the causes of extubation are required to further reduce this incidence.