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Actinomycosis is an uncommon disease, which is usually manifested as cervicofacial infection and related to poor oral hygiene or compromised immune function. Pulmonary actinomycosis is rare, but its diagnosis is changing due to its variable presentation and the similarity in appearance to other intrapulmonary diseases. Here we report a 48-year-old febril neutropenic man who had the diagnosis of Acute Lymphocytic Leukemia (ALL), under treatment of pneumonia for 3 weeks. He had also poor oral hygiene and gingivitis. He was consulted by Pulmonology department becauseof the presence of fever under antibiotherapy and perihiler cavitary infiltration on chest X-ray. Thoracal Computerized Tomography was offered which revealed a thick-walled cavitary lesion in the base of the anterior segment of right upper lobe with surrounding consolidation. Fiberoptic bronchoscopy was performed and bronchial and bronchoalveolar lavage was sampled for exact diagnosis. Histological examination demonstrated Sulphur granules, revealing this patient had an Actinomyces infection. Sulbactam-Ampicillin treatment was planned. Clinical response was seen within first week. Laboratory (C-reactive protein) and radiological findings regressed in the first month. Fifth month’s tomographic findings were only traction bronchiectasis and fibroatelectatic changes in right upper lobe. Antibiotic treatment was stopped then. He’s still under follow-up of Hematology department. Pulmonary actinomycosis can be a difficult condition to diagnose with delayed diagnosis or misdiagnosis, being common. Isolated pulmonary involvement is rare. Diagnosis of actinomycosis hinges on clinicomicrobiological correlation and response to specific treatment. While pulmonary actinomycosis has rarely been reported in literature, we conclude that it should be kept in mind especially in immunocompromised patients with poor oral hygiene.