BACKGROUND The incidence of bronchial hyperreactivity has increased to one-third of the population in developed countries, which requires the adoption of preventive and therapeutic measures. The objective of the present study was to assess the effects of a traditional Mediterranean diet on patients diagnosed with childhood asthma and determine if there is a beneficial effect from this dietary intervention. METHODS Prospective before-after comparison study of 50 girls and 54 boys aged 1-5 years, who were enrolled in the 1-year programme "Learning to Eat from the Mediterranean", designed to promote the adoption of a traditional Mediterranean diet. We studied the clinical and therapeutic variables and anthropometric measurements. RESULTS All studied symptomatic indicators (number and intensity of asthmatic attack, infections and hospital admissions) showed a positive and statistically significant evolution of bronchial hyperreactivity from the first weeks of the intervention onwards. Throughout the treatment, 32.2% of patients remained free of crisis, 35.3% of the patients only had one attack throughout the year and 24.9% had two episodes, compared to 4.73 episodes on average in the previous year. The use of inhaled corticosteroids markedly decreased from 3.92 ± 1.61 to 1.11 ± 1.09 times per patient per year (P<0.001) and that of inhaled bronchodilators decreased from 4.14 ± 1.61 to 1.12 ± 1.40 (P<0.001). As a result, the families involved in the programme reported a high level of satisfaction. CONCLUSIONS The adoption of a traditional Mediterranean diet could contribute significantly to the improvement of patients diagnosed with childhood asthma.