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INTRODUCTION: Interstitial Lung Disease(ILD) is a serious complication of Mixed Connective Tissue Disorder(MTCD) associated with high morbidity and mortality. We describe an unusual case of a young patient presenting with advanced fibrosis at the time of initial diagnosis of MTCD. CASE PRESENTATION:A 39 year old female presented with dyspnea and dry cough of four months duration that progressively worsened requiring assistance for daily activities. She had associated weight loss, night sweats, diffuse arthralgia without any swelling and right hand stiffening. She denied any fevers, oral/nasal ulcers, vision changes, recent travel, tick bites, skin rash, smoking, household mold or pets. Physical examination revealed bibasilar crackles and mild dusky appearance of fingers. Laboratory investigations showed a normal blood count, elevated d-dimer and inflammatory markers. High Resolution Computerized Tomography(HRCT) Scan of the chest showed diffuse ground glass opacities, subpleural reticulation/scarring, traction bronchiectasis with multiple areas of honeycombing as well as extensive mediastinal lymphadenopathy. The serological panel was significant for high titers of Anti-Nuclear Antibodies(ANA) 1:1280 speckled pattern with low complement C3/C4 level, Rheumatoid Factor(RF) 138, Immunoglobulin G(IgG) 5000, anti-SSA and anti-ribonucleoprotein antibodies 133 and 148 respectively, elevated aldolase and creatinine kinase. Infectious workup was negative. The diffusely positive serology and lymphadenopathy was concerning for lymphoma. However, the excisional lymph node biopsy was negative for malignancy and showed changes consistent with autoimmune etiology. She was diagnosed with MTCD with features of lupus, sjogrens, rheumatoid arthritis, myositis presenting as ILD. Treatment with steroids and hydroxychloroquine was initiated with improvement in her respiratory symptoms. DISCUSSION: ILD in patients with MTCD ranges from being asymptomatic to advanced fibrosis with a high mortality rate.Typically, intial pulmonary function testing shows reduced diffusion capacity which progresses to restrictive pattern in the later stages along with HRCT changes. Our patient, although young, had rapid progression of pulmonary symptoms and was found to have advanced scarring on initial presentation. The diffusely positive serology can overlap with lymphoma and biopsy of lymph node/lung can give definite diagnosis. Since screening guidelines for MTCD-ILD are not clearly established any clinical symptoms should prompt further investigations. Treatment especially steroids during the acute inflammatory phase with ground glass opacities has good prognosis whereas the response is poor once signs of fibrosis develop.CONCLUSIONS: Advanced fibrosis ILD is an uncommon presentation of MTCD in a young patient. Early diagnosis and prompt initiation of therapy especially during the acute phase can prevent further progression of disease.