en Pulmonology Pulmonology case report case report Background: In many cases of ILD (interstitial lung disease), overlap diagnosis is considered. Here, a few cases with diagnosis of a variety of ILDs, where eventual open lung biopsy has been performed are selected. Reference will be made to reliable sources to show that NSIP can still be a variant of UIP (Usual interstitial pneumonia) with better treatment response and prognosis. Case Presentation: In case 1, there is a difference between the HRCT(High Resolution Computed Tomography) result (NSIP pattern without fibrosis) and pathologic result (which includes fibrosing NSIP more closely related to UIP).Case 2 shows obvious discord between HRCT result (UIP pattern) and pathologic result (NSIP pattern). In case 3, there is again a discrepancy between HRCT report (very mild architectural distortion suggestive for ILD like NSIP) and pathology report (destructed lung tissue with interstitial fibrosis suggestive of HP (Hypersesitivity Pneumonitis) and not NSIP. Conclusion: In this paper, we demonstrate that although NSIP can be a distinct diagnosis in most cases, but in rare cases the distinction between the other kinds of ILD especially UIP and NSIP in spite of full workup including tissue assessment can be very difficult. Lung Diseases, Interstitial Pneumonia, Diagnosis, Computed tomography 118 122 http://caspjim.com/browse.php?a_code=A-10-62-180&slc_lang=en&sid=1 Payam Mehrian 10031947532846001316 10031947532846001316 No Pediatric Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran Ali Cheraghvandi 10031947532846001317 10031947532846001317 No Lung Transplantation Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran Atousa Droudnia 10031947532846001318 10031947532846001318 No Tracheal Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran. Firouzeh Talischi 10031947532846001319 10031947532846001319 No Nursing and Respiratory Health Management Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran. Saeid Fallah Tafti 10031947532846001320 10031947532846001320 Yes Tobacco Prevention and Control Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences,Tehran, Iran. Shahram Kahkouee 10031947532846001321 10031947532846001321 No Mycobacteriology Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran. Hamidreza Jamaati 10031947532846001322 10031947532846001322 No Chronic Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran