Interstitial lung diseases (ILD) are difficult to diagnose and to classify. Despite symptoms and clinical findings typical for ILD, a broad differential diagnosis must be kept in mind. Multidisciplinary discussion (MDD) contributes to correct diagnosis and is therefore considered the diagnostic gold standard in ILD. Here we report on three patients that were referred to our ILD clinic with suspected ILD. They all presented with chronic dyspnea on exertion, cough and abnormal lung function tests showing reduced diffusing capacity as well as hypoxemia. Chest CT scans were compatible with ILD. Further diagnostic workup was performed, revealing two adenocarcinomas of the lung and one malignant B cell lymphoma. In summary, despite clinical, physiological and radiological presentation typical for ILD, further workup is needed early in the course of the disease to rule out possible differential diagnoses including malignancies.