Summary Background Patients with chronic hypersensitivity pneumonitis (HP) can present with an insidious onset of their disease without typical fluctuating flu-like symptoms, and there are only signs of chronic respiratory failure caused by the progressive fibrotic lung disease. Case Report A 45-year-old man with a pneumomediastinum and interstitial lung disease was referred for further investigations and therapy. No traumatic event or interventional procedure had occurred prior to referral. The patient had been working in farming for almost 20 years and was exposed in childhood by his father to pigeon breeding from childhood until 20 years ago. He reported dyspnea on exercise for the previous 2 years. High-resolution CT of the lung showed a pneumomediastinum and a fibrotic interstitial lung disease without dominating ground-glass opacities. Specific IgG antibodies were markedly elevated against molds and avian antigens. Bronchoalveolar lavage demonstrated a slightly lymphocytic and neutrophilic alveolitis. After recovering from the pneumomediastinum, an open lung biopsy was performed and a UIP-pattern was detected. An inhalative challenge with hay from the work-place was positive. A diagnosis of chronic farmer’s lung was made. Conclusions Pneumomediastinum has been described in other fibrotic lung diseases, but until now it has not been described as a primary manifestation of chronic fibrotic HP. Particularly in cases of concurrent antigen sources, an inhalative challenge could be done, even in a chronic course of HP.