Our previous studies have reported that the prevalence of asthma was 2.89% and of allergic rhinitis 1.54% in Ligurian conscripts for the army during 1983. Since several authors reported an increasing prevalence of these diseases in different geographic areas, the aim of the present study was to evaluate the trend of prevalence rates in a same homogeneous group of Ligurian conscripts. The prevalence of asthma and allergic rhinitis was assessed in a group of 4310 young Ligurian men (18 years old) who had undergone medical examination for call-up to the navy during 1993, 1994 and 1995. Subjects were investigated by history, clinic visit, spirometry, metacholine bronchial challenge and skin prick test. The prevalence of asthma is 4.39% and of allergic rhinitis 2.2%. Comparing these results with previous data, a significant increase appears in this area 12 years later (respectively, p < 0.001 and p < 0.006). In addition, the association with asthma in allergic rhinitics increases from 41 to 77%, as well as an increasing trend appears for perennial allergens (i.e. mites and cat) and the polysensitizations increase from 48 to 67%. Possible explanations for these phenomena might be due to environmental factors (i.e. pollutants, viral infections, changes in domestic microenvironment).