Few published studies have compared epidemiological data on the prevalence, incidence or relative frequency of the different interstitial lung diseases. In this review, the data of such registries from three countries in Europe (Belgium, Germany and Italy) are compared with those in the USA (Bernalillo County, NM). These registries show some striking similarities, but also discrepancies, which in part may be real, but may also be due to selection bias. Indeed, the registries in the European countries encompass the patients seen by pulmonologists, while the registry in Bernalillo County is based on a general population study in a limited area. In addition, in some studies, prevalences and incidences were registered, while in others, only prevalences or incidences were registered. Finally, most, but not all studies were prospective. Nonetheless, the different studies showed that sarcoidosis, idiopathic pulmonary fibrosis, hypersensitivity pneumonitis, interstitial lung diseases due to collagen vascular diseases and not-defined (or postinflammatory) fibrosis were most frequent. In the majority of disease entities a male predominance was found. Surprisingly large differences in the use of diagnostic techniques, such as high-resolution computed tomography, bronchoalveolar lavage, open lung biopsy and transbronchial lung biopsy, were noted between the different studies.