RIPID was established in 1998 as a joint project of the major Italian scientific societies for Respiratory Medicine, with the aim to create an Italian Register on diffuse infiltrative lung disorders that can provide the basis for epidemiological and clinical studies of adequate sample size. In the period from May 1998 to December 2000, 1,382 cases were submitted from 54 Centers in 15 regions of Italy, 54.2% males (mean age +/- SD 50.5 +/- 16.8 years) and 45.8% females (50.2 +/- 15.3 years). A current smoking habit emerges in 18% of subjects; former smokers and never-smokers represent 26% and 56% of the total case series, respectively. The most frequent disease registered is idiopathic pulmonary fibrosis (37.6%), followed in decreasing order by sarcoidosis (29.2%), and Langherans' cell hystiocytosis (6.6%). High resolution computed tomography (HRCT) was considered as the most important tool for final diagnosis in the majority of cases (74.4%); 39.4% of patients underwent transbronchial biopsies, 39.2% bronchoalveolar lavage (BAL). A surgical biopsy was performed in 20.5% of patients. A web site has been activated from December 2000 (www.pneumonet.it/ripid), allowing prompt access to all information and scientific material concerning the project and to an electronic form for data collection that can be completed on-line.