This study analyzes the evolution of a group of children under 10 years of age with asthma over a period of 20 years. We selected a random group of 32 children with asthma and compared it with a control group composed of 33 children without asthma, similar in age, sex, and socio-economic characteristics. Throughout the 20 years we analyzed the number of ambulatory visits, morbidity, environmental tobacco smoke (ETS) as well as social and economic characteristics. The results after 20 years of evaluation showed that inflammatory and infectious processes in the airways (upper and lower) were more frequent among asthmatics than in the control group. ENT infections were more predominant in the group with inadequate sanitary conditions. There were no significant differences for the other pathologies. We studied the frequency of asthmatic crises requiring emergency care according to age and sex. Clinical ambulatory visits in asthmatic children were 2.8 times more frequent than in the control group. We found no differences between males and females, either in terms of global morbidity or the worsening of their asthmatic disease e.g., crises, going to emergency services and hospitalization. In the asthmatic group, the frequency of asthma crises, visits to emergency services and hospitalization were analyzed, with no differences being found between the sexes. We measured the PEFR, FEV1, and FEF25-75 in both groups for 20 years and compared those values to age, weight, height, and sex. We found that the parameters of lung function were lower in the asthmatic group than in the control group. We used as statistical method the chi 2 test, and regression analyses were made to relate the PEFR, FEV1, and FEF25-75 values to age and gender. A paired t-test was used to compare ambulatory visits, morbidity, emergency care, ETS, and sanitary housing conditions to age and sex in both groups. A p value < or = 0.05 was taken as indicating statistical significance.