Objective To provide clues to diagnosis and treatment for diffuse alveolar hemorrhage (DAH)in patients with diffuse connective tissue diseases(CTD).Method To analyze restropeetively the data of clinical features,pulmonary images and bronchoalveolar lavage(BAL)in 32 patients hospitalized in Peking Union Medical College Hospital from April 2004 to June 2007.Results The data from 1O of the 17 (58.8%)patients with microscopic polyangiitis(MPA),19 of the 1267(1.5%)patients with systemic lupus erythematosus(SLE),2 of the 56(3.6%)patients with Wegener's granulomatosis(WG)and 1 of the 570(0.2%)patients with rheumatoid arthritis(RA)were consistent with the diagnosis of DAH.DAH in SLE occurred in younger patients(mean age at the time of diagnosis 27.3±13.1 years)and early in the course of disease(median duration of SLE from onset was 16.7±18.3 months),while these figures in MPA patients with DAH were 50.1±20.7 years and 10.6±18.7 months.At the time of DAH in SLE.the median systemic lupus erythematosus disease activity index(SLEDAI)score was 17.1±6.7 and anti-ds-DNA antibody titer elevated markedly,while the median C3 level was low.The levels of erythrocyte sedimentation rate(ESR)and C-reactive protein(CRP)of patients with DAH in MPA,WG and RA showed marked elevation.The titer of antieutrophil cytoplasmic antibody(ANCA,MPO/PR3)in patients with MPA and WG was highly positive.The main clinical manifestations of DAH were hemoptysis,dyspnea and rapid decrease of hemoglobulin and hematoerit(HCT)in peripheral blood.Most patients presented with difluse alveolar infiltration on chest X-ray and hish resolution CT.DAH could be confirmed by bloody bronchoscopic lavage.20 patients(62.5%)had secondary pulmonary infections at the time of DAH;fungus and combined bacterial infection were most frequently seen.The mortalitv 0f CTD with DAH was 59.4%(19 out of 32).12 patients (63.2%)with SLE,5 patients(50%)with MPA and both of the 2 patients with WG died.12 of the lethal cases(63.2%)died of respiratory failure.Conclusions CTD patients presenting with hemoptysis and dyspnea with rapid decrease of hemoglobulin,and diffuse alveolar infiltration on chest X-ray or high resolution CT should be seriously considered to be suffering from DAH.A bloody BAL may confirm the diagnosis of DAH.DAH in CTD is an acute,serious and frequently life-threatening situation resulting in respiratory hilure and pulmonary infection.It is important for CTD patients with DAH to be diagnosed early and treated vigorously.