OBJECTIVE To present the onset of severe pulmonary arterial hypertension (PAH) in a patient with interstitial lung disease (ILD) associated with overlap syndrome. CASE PRESENTATION A 42-year-old female was diagnosed with overlap syndrome consisting of systemic lupus erythematosus (SLE), systemic sclerosis (SSc) and rheumatoid arthritis (RA). The serologic profi le included positive antinuclear antibody (ANA), anti-dsDNA, anti-RNP, anti-Ro, anti-Scl70, anti-Sm, rheumatoid factor and hypocomplementemia (C3, C4). She had chronic stable ILD for 17 years maintained on hydroxychloroquine (HCQ), prednisone 5 mg/day and indacaterol. The current admission was due to progressive dyspnea and right-sided heart failure over the past month. Chest radiograph showed pulmonary congestion, and 2-dimensional echocardiography (2DE) disclosed severe PAH with systolic pulmonary arterial pressure (SPAP) of 76 mmHg by tricuspid regurgitation (TR) jet, dilated right ventricle (RV) with poor systolic function, moderate pericardial effusion with no signs of tamponade. She received furosemide, beraprost, sildenafi l, and prednisone was increased to 20 mg/ day. Two weeks following discharge, there was complete resolution of symptoms and repeat 2DE showed non-dilated RV with good systolic function, normal SPAP of 21.4 mmHg and minimal pericardial effusion. Prednisone was tapered to 5 mg/day; beraprost, sildenafi l and HCQ were continued. CONCLUSION Overlap syndrome was diagnosed by the combination of clinical features and serology distinctive of SLE, SSc and RA. Her illness, particularly ILD, was adequately controlled over several years, until the recent onset of PAH complicated by right-sided heart failure. The dramatic response to high-dose steroids is more consistent with infl ammatory vasculitis of SLE activity rather than fi brosis typical of SSc.