I was extremely fortunate in my ID rotation and some of the rare infections on my list of “would like to see” manifested in hospital during my ID rotation. This included fungal lung infections. The culture was +1 for aspergillus of a lung biopsy and it provided me an opportunity to clarify a burning therapeutic question and that was how to assess these culture results? In a patient with respiratory disease, one of two things could be happening. Firstly, aspergillus is an environmental mold and isolation from sputum or lung tissue biopsy does not necessarily indicate invasive disease of the lung parenchyma. This may be a commensal with no implication in the current clinical status of the patient. Although the sequelae of an untreated invasive or chronic aspergillosis may be serious, the antifungals to treat aspergillus have potentially toxic side effects, serious drug interactions and long durations of treatment. So understanding when and when not to treat is an important part of medication management. I recalled a case early in my residency where a deep sputum culture grew +1 aspergillus however unlike this patient no treatment was recommended. In the end, it came down to careful consideration of the patient specific factors including history, risks and comorbidities.