Pulmonary alveolar microlithiasis (PAM) is a rare chronic disease of unknown etiology and pathogenesis. The disease is characterized by the diffuse presence in the alveoli of minute calcific deposits known as microliths. In most cases patients have mild clinical symptoms, contrasting with the severe radiographic appearance: this is a typical feature that should raise the suspicion of PAM. The first to describe the clinical and radiographic aspects of the disease, as well as the first case series, was the radiologist Sosman. In recent years, high resolution computed tomography (HRCT) has made it possible to define the extent and severity of the disease more precisely, and has demonstrated calcifications in anatomical sites that could not be shown by conventional radiology. The present paper describes the radiological evolution of the disease, and suggests a classification based on the radiographic and HRCT follow-up of the three clinical cases: two young patients followed up for 24 and 11 years and one elderly man who is still alive and is the PAM case with the longest survival since diagnosis, over 50 years, to be reported in the international literature.