The study of disease prevalence requires specific and sensitive indicators, which are hardly gathered at population level. The use of anti-asthma drugs, which are relatively specific for diseases characterised by bronchospasms, has been already experimented in the USA with algorithms describing patients affected by asthmatic disease by their use of drugs. We retrospectively analyse spatial variations of drug use as dispensed by the SSN (National Health Service) to Lombardy children less than 15 years old, between 1st January 1995 and 31st December 1997, estimating prevalence of use as a proxy of disease prevalence. Two algorithms already experimented and a new one have been employed to select children treated with antiasthmatic therapy (R03 of ATC classification) dispensed. Local communities' data were used for basic demography. Number of daily defined doses (DDD) dispensed has been used as indicator of drug quantity. Euro/year per person has been used as indicator of costs. Small area distribution analysis has been performed with a Geographic Information System at local Communities level. Frequency of patients (of a total of 1,252,958 children): with at least one dispensed drug in the three years was 26.6% (SD 10.5), DDD per person per month were 1.21 (SD 0.78), Euro/Year per person 6.84 (SD 3.61); with the association of a anti-inflammatory and a b2-agonist was 8.2% (SD 5.6), DDD per person per month were 3.01 (SD 3.07), Euro/Year per person 15.87 (SD 15.07); with at least 90 days of DDD in the three years was 2.6% (SD 1.3) DDD per person per month were 7.79 (SD 4.48), Euro/Year per person 37.66 (SD 21.83). It must be taken into account that, in the best of cases, these approximation refers to the prevalence of all diseases, characterised by bronchospasm, treated with the selected drugs. Estimated data of prevalence are comparable with those of other authors. Prevalence of drug use appears to have relevant geographical differences. Taking into consideration these comments, prevalence of drug use and consequently the estimated disease prevalence appears to be worryingly high, having as well wide geographical differences.