As discussed in Chap. 39 , despite all reasonable investigation, Microbiological identification is not possible in about 60% of all cases of community-acquired pneumonias. In some cases where the resolution is slow, a large number of possibilities become open to active consideration. This chapter incorporates a methodical approach to slowly resolving or nonresolving infiltrates of the lung and raises issues to consider when the pneumonia is slow to resolve. It explores the wide range of non-infectious conditions that might masquerade as a pneumonia and attempts to seek out and clarify any local or systemic factors that might be interfering with resolution of a true pneumonia, or any antibiotic resistance that might be present. The chapter also provides insight into the cause of recurrent pneumonias based on the site and pattern of recurrence, and presents information that is of utility in formulating a rational diagnostic approach in such circumstances.