The prevalence of asthma and allergies among children has become an increasing problem in the last few decades. Data on the population of children and adolescents, especially living in polluted cities, are limited and based on studies carried out in small groups. In our study, we analyzed the incidence of asthma and allergic rhinitis between 2014 and 2018. We analyzed data collected from nearly 30,000 children aged seven to eight and adolescents aged 16–17, which allowed us to assess the frequency of allergic diseases in the population of children and youth in Krakow. More than 40% of respondents reported allergic symptoms, and nearly 50% of them were not diagnosed and treated. In the group of seven- and eight-year-olds with a positive history of allergies, 52% had allergic rhinitis and 9.1% had asthma. In the group of 16–17-year-olds, allergic rhinitis was diagnosed in 35.8%, while asthma was found in 4.9% of cases. The results obtained over the course of 10 years has shown the reduction in the frequency of asthma (from 22% in the case of asthma in both age groups) and allergic rhinitis cases (from 63.9% in adolescents). In our opinion, this can be considered a positive effect of the preventive measures taken in Kraków after 2010. Although there is still a higher incidence of allergic diseases among children and young people living in urban areas compared to rural areas, the trend apparently has reversed for some diseases.