Empyema necessitatis is a relatively rare entity. Two instances of mastitis secondary to empyema necessitatis, diagnosed by fine needle aspiration biopsy are reported. One case was tuberculous in etiology and was initially recognized by cytologic findings of epithelioid and granulomatous cellular reactions and the presence of acid-fast bacilli, which were subsequently cultured and speciated as Mycobacterium tuberculosis. The other case was due to coexisting Actinomyces and Actinobacillus. These organisms were cytologically suggested by "sulfur" granules of filamentous, gram-positive bacilli, admixed gram-negative coccobacilli and Splendore-Hoeppli phenomenon in an exudative cell background and were confirmed by microbiologic culture as Actinomyces israelii and Astinomyces actinomycetemcomitans, respectively. The usefulness of fine needle aspiration cytology in the diagnosis of empyema necessitatis, supported by ancillary microbial culture, histochemistry, and radiographic imaging, is well illustrated by these two cases.