OBJECTIVES: A few epidemiological studies have indicated that a patient\'s past medical history may contribute to the risk of developing idiopathic pulmonary fibrosis (IPF). A relationship between a history of selected disorders and the risk of IPF was assessed in a multicentre hospital-based case-control study in Japan. METHODOLOGY: Included in the study were 104 patients of IPF, aged 40 years or over, who had been diagnosed within the previous 2 years, in accordance with the most recent criteria. Control subjects, aged 40 years or over, consisted of 56 hospitalized patients diagnosed as having acute bacterial pneumonia and four outpatients with the common cold. Adjustment was made for age, gender, region, pack-years of smoking, employment status, occupational exposure and BMI. RESULTS: Medical histories of hypertension, hyperlipidaemia, coronary heart disease, diabetes mellitus, hepatitis C virus infection, tuberculosis, asthma, atopic dermatitis and allergic rhinitis were not statistically significantly associated with the risk of IPF, although cases were more likely to have suffered from allergic rhinitis and less likely to have been asthmatics than control subjects. Having a child with a history of allergic rhinitis, but not of asthma or atopic dermatitis, was significantly related to an increased risk of IPF. CONCLUSIONS: These findings suggest that a genetic predisposition to allergic rhinitis may be associated with an increased risk of IPF.