Tube thoracostomy is a standard method of treating pediatric parapneumonic collections. Despite recent work denoting thoracoscopy as a superior method of treatment, few studies have looked at factors predictive of tube thoracostomy failure. We reviewed parapneumonic collections initially treated with tube thoracostomy to identify such factors.Nontuberculous parapneumonic collections treated initially with tube thoracostomy over a 10-year period were reviewed. A “failed primary tube thoracostomy” was defined as the presence of worsening clinicoradiological signs requiring a further chest procedure (ie, thoracoscopy, thoracotomy, or second thoracostomy).Fifty-eight patients were identified. Forty-three percent failed primary tube thoracostomy. Within group F (failure group), 32% of patients had a concomitant medical condition (P < .001). Sixty percent of group F patients had duration of symptoms for more than 1 week compared with only 24% of group S (successful group) (P < .001).Our results suggest that primary treatment of parapneumonic collections with tube thoracostomy is likely to be unsuccessful in patients who are symptomatic for more than a week or who have a concomitant medical condition.A more aggressive primary surgical intervention is suggested for this group.