Pulmonary inflammation and the development of spontaneous lung tumors are important age-related lesions in mice. Therefore, gross and histological examination of the respiratory system is a critical component of geropathology research studies for translating surrogate endpoints to clinical aging studies. Collection, trimming, and processing of lung tissue from aged mice require a high-quality sequential process since aged mice are irreplaceable resource-intensive animal models. This protocol provides a basic technique that provides excellent sections for histological evaluation of the respiratory system of old mice suitable for most research applications. The points of emphasis are infusing the lungs at necropsy with formalin through the airways to prevent atelectasis artifacts that can preclude accurate histological evaluation, and embedding of anatomically oriented in toto lung lobes to allow for complete and thorough evaluation of all lung regions.