The International Study of Asthma and Allergy in Childhood (ISAAC) has assessed the prevalence of asthma, as well as the factors related to the disease in different countries. The aim of this study was to identify asthma risks factors in Mexico City. Data were obtained from questionnaires of children participating in a phase 3b ISAAC survey. Two thousand ninety-eight boys and 2008 girls were recruited in the 6- to 7-year-old group and 3243 boy and 3333 girls were recruited in the 13- to 14-year-old group. Logistic regression was used to determine the asthma risks factors. In the logistic regression for cumulative and current asthma prevalence, the variables allergic rhinitis and atopic dermatitis were the most important risk factors with the highest odds ratios (OR > 1.5; p < 0.05). The use of antibiotics and paracetamol in the first 12 months of life were related to cumulative asthma in both genders in the 6- to 7-year-old group. Contact of pregnant mother with farm animals was positively related with cumulative asthma in boys in the 6- to 7-year-old group. The main factors associated with the cumulative and current prevalence of asthma in both age groups were atopic dermatitis and allergic rhinitis. Future interventions for the prevention and early diagnosis and treatment could be focused in the natural history of the atopic march.