There is a lack of knowledge to which extent heredity or familial risk factors are involved in the development of chronic bronchitis/emphysema (CBE). Smoking is regarded as the most important risk factor, but only about 15% of smokers develop airway obstruction. We evaluated the importance of familial risk factors compared to smoking and ex-smoking using an epidemiological approach. In 1992, a postal questionnaire was distributed to a study sample. In all, 43 questions were asked, in a previously evaluated questionnaire, regarding respiratory symptoms, self-reported lung diseases, smoking habits and familial occurrence of chronic bronchitis and asthma. The questionnaire was sent to 12,073 adults living in the southernmost part of Sweden. The age range was 20-59 years with an equal gender distribution. The study sample was drawn from the population records. The questionnaire was answered by 8469 subjects (70.1%), of whom 392 subjects (4.6%) stated that they had or had had CBE and 469 subjects (5.5%) stated that they had or had had asthma. In a model with logistic regression using the five explanatory variables gender, age, familial occurrence for asthma, familial occurrence for CBE and current or ex-smoking the most important risk factors for CBE were familial occurrence for chronic bronchitis [Odds ratios (OR): 5.19, 95% confidence interval (CI): 4.09-6.60, p = 0.000] and current or ex-smoking (OR: 1.74, 95% CI: 1.41-2.14, p = 0.000). The most important risk factors for asthma were familial occurrence for asthma (OR: 3.71, 95% CI: 3.06-4.51, p = 0.000) and current or ex-smoking (OR: 1.33, 95% CI: 1.09-1.61, p = 0.004). We have found that familial occurrence for CBE in first degree relatives together with smoking is a stronger risk factor for the development of CBE than is smoking.