Abstract. OBJECTIVE: Antenatal, postnatal follow-ups and laboratory findings of the cases with retained fetal lung fluid syndrome were evaluated to detect prognostic factors. STUDY DESIGN: This study was conducted at Zeynep Kamil Maternity and Children’s Training and Research Hospital including infants retained fetal lung fluid syndrome. Patients were divided into 3 groups according to duration of the clinical symptoms. Cases whose clinical findings resolving within first 24 hours constituted Group 1 (n = 31), cases with clinical findings persisting between 24 and 72 hours constituted Group 2 (n = 95) and cases with symptoms persisting >72 hours constituted Group 3 (n = 10). Antenatal and postnatal clinical data and laboratory findings of the patients were evaluated retrospectively. RESULT: Pneumothorax, pulmonary hypertension, antibiotic use frequency and hospitalization periods were found to be prolonged in the patients admitted due to retained fetal lung fluid syndrome who were delivered with elective caesarean section, with low birth weight and gestational age, requiring intubation and invasive ventilation within first 12 hours, having low hemoglobin and blood chloride levels. CONCLUSIONS: Low blood chloride level can be a laboratory finding predicting whether malignant tachypnea develops or not in retained fetal lung fluid syndrome. Cut-off chloride value for malignant tachypnea can be determined with new studies which will be performed in the future.