To determine the pneumological causes for hospital admission in Andalucia (Spain) and thereby improve knowledge of respiratory morbidity. From the Combined Minimum Data Base on admissions to Andalusian hospitals for 1993 and 1994, adjusted to the CIE-9-MC coding system, we analyzed main diagnoses registered. Cases with respiratory involvement were obtained, excluding patients under 7 years of age. Admissions for pneumological causes accounted for 6.3% of all admissions, with a total of 314 diagnostic categories, although 98.5% of all admissions were related to only 139 diagnoses. The 53 most frequent diagnostic categories accounted for 93% of patients and 55.2% of admissions were related to only 10 causes and led to 54.16% of all stays for pneumological diseases. Categories 486 and 481 (pneumonias), along with 496, 491.2 and 491.21 (diseases involving chronic air flow obstruction) were the most often used. Respiratory problems account for 6.23% of all hospital admissions in Andalucia, with lung infections and conditions falling under the category of chronic obstructive pulmonary disease being by far the most frequent pneumologically related reasons for hospitalization. The precise interpretation of diagnostic categories needs to be better defined in the coding system.