Background: Patients with malignant pleural effusion (MPE) secondary to lung cancer have been associated with poor prognosis historically. LENT score developed to risk-stratify unselected patients with MPE predicts prognosis of < 6 months in patients with lung cancer. Objective: To assess the performance of LENT score in predicting prognosis in selected population of MPE secondary to lung adenocarcinoma alone. Methods: A retrospective observational study was conducted by reviewing the medical records of patients managed for MPE in the year 2012. Results: Seventy patients with lung adenocarcinoma presenting with MPE were studied. The median (range) LENT score at initial diagnosis was 5 (2–7), and the median survival 7.9 (0.13–40) months. Thirty-nine patients received epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKIs). The median LENT score and median survival was 4 (2–7) and 14.4 months, respectively, in this group. Those in high-risk category by LENT in this group (n = 19) had a median survival and 6-month survival of 17.4 months and 73.6%, respectively. Thirty-one patients were treated with conventional chemotherapy. The median LENT score and median survival was 5 (2–7) and 4.1 (0.13–34.3) months, respectively, in this group. The median survival and 6-month survival rate in patients in high-risk category and moderate-risk category by LENT score was 6.2 months and 52.7%, and 11.4 months and 70.5%, respectively. Conclusion: LENT score underestimates prognosis in patients having MPE secondary to lung adenocarcinoma. This disparity particularly applies to the lung adenocarcinoma patients carrying EGFR mutation. Hence, LENT score may not be applicable to, or may need modification before applying to such patients.