ABSTRACTPAP is an ultra‐rare disease in which surfactant components, that impair gas exchange, accumulate in the alveolae. There are three types of PAP. The most frequent form, primary PAP, includes autoimmune PAP which accounts for over 90% of all PAP, defined by the presence of circulating anti‐GM‐CSF antibodies. Secondary PAP is mainly due to haematological disease, infections or inhaling toxic substances, while genetic PAP affects almost exclusively children. PAP is suspected if investigation for ILD reveals a crazy‐paving pattern on chest CT scan, and is confirmed by a milky looking BAL that gives a positive PAS reaction indicating extracellular proteinaceous material. PAP is now rarely confirmed by surgical lung biopsy. WLL is still the first‐line treatment, with an inhaled GM‐CSF as second‐line treatment. Inhalation has been found to be better than subcutaneous injections. Other treatments, such as rituximab or plasmapheresis, seem to be less efficient or ineffective. The main complications of PAP are due to infections by standard pathogens (Streptococcus, Haemophilus and Enterobacteria) or opportunistic pathogens such as mycobacteria, Nocardia, Actinomyces, Aspergillus or Cryptococcus. The clinical course of PAP is unpredictable and spontaneous improvement can occur. The 5‐year actuarial survival rate is 95%.