Objective By comparing the clinical characteristics, etiological characteristics, laboratory examination and prognosis of community acquired pneumonia (CAP) patients with and without pleural effusion (PE), the risk factors affecting the 30-day mortality of CAP patients with PE were analyzed. Methods The clinical data of inpatients with CAP in 13 hospitals in different regions of China from January 1, 2014 to December 31, 2014 were analyzed retrospectively. According to the imaging examination, the patients were divided into two groups: PE group (with pleural effusion) and non-PE group (without pleural effusion). The clinical data, treatment, prognosis and outcome of the two groups were compared. Finally, multivariate analysis was used to analyze the risk factors of 30-day mortality in patients with PE. Results Of the 4781 patients with CAP, 1169 (24.5%) were PE patients, with a median age of 70 years, and more males than females, having smoking, alcoholism, inhalation factors, long-term bed rest, complicated with underlying diseases and complications, such as respiratory failure, acute respiratory distress syndrome (ARDS), cardiac insufficiency, septic shock, acute renal failure and so on. The hospitalization time was prolonged; the intensive care unit (ICU) occupancy rate, mechanical ventilation rate, mortality within 14 days and mortality within 30 days in the PE group were higher than those in the non-PE group. Multivariate analysis showed that the risk factors affecting 30-day mortality in the patients with PE were urea nitrogen >7 mmol/L (OR=2.908, 95%CI 1.095 - 7.724), long-term bed rest (OR=4.308, 95%CI 1.128 - 16.460), hematocrit <30% (OR=4.704, 95%CI 1.372 - 16.135), acute renal failure (OR=5.043, 95%CI 1.167 - 21.787) and respiratory failure (OR=6.575, 95%CI 2.632 - 16.427), ARDS (OR=8.003, 95%CI 1.852 - 34.580). ConclusionsThe hospitalization time and ICU stay of PE patients are prolonged, the risk of complications increases, and the hospital mortality increases significantly with the increase of age, complication and disease severity. The independent risk factors affecting 30-day mortality in PE patients are urea nitrogen >7 mmol/L, long-term bed rest, hematocrit <30%, acute renal failure, respiratory failure, and ARDS.