An enquiry was made to determine the prevalence of asthma in adolescents and was achieved using a questionnaire which was filled in by the pupils in secondary schools in Rabat. The sample was determined by a systematic poll of 1,616 pupils of whom 1,464 (90.6%) replied. 88 pupils (6.0%) replied in the affirmative to the question "Have you ever had whistling noises in the chest?", 78 (5.3%) to the question "Have you ever had a sensation of respiratory difficulty or suffocation with a whistling noise in the chest?", 48 (3.3%) to the question "Have you ever had asthma?" and 36 (2.5%) to all 3 questions and 114 (7.8%) to one or other of the questions. After a detailed questionnaire had been carried out on 110 of 114 pupils the diagnosis of asthma was confirmed in 50, which gives an estimation of the accumulative prevalence of 3.4% +/- 0.9%. This prevalence is higher amongst the oldest children in the family (26 out of 349, 7.4%) compared to the birth order of the other brothers and sisters (24 out of 1,112, 2.2%) (p less than 0.001). Pupils from higher social backgrounds (22 out of 256, 8.6% against 28 out of 1,208, 2.3% from more average or more poor social backgrounds, p less than 0.01). A past family history of asthma were more often noted in asthmatics (38 out of 50, 76%) than in non-asthmatics (406 out of 414, 28.7%) p less than 0.001). In the same way cough and phlegm and episodes of bronchitis occurring in autumn and winter and breathlessness on effort are more frequent in asthmatics; 20 out of 50 (40%) against 318 out of 1,414 (22.5%) for the cough (p less than 0.01), 12 out of 50 (24%) against 157 out of 1,414 (11.1%) for phlegm (p less than 0.01), 31 out of 50 (62%) against 337 out of 1,414 (23.8%) for episodes of bronchitis (p less than 0.001) and 15 out of 50 (30%) against 219 out of 1,414 (15.5%) for breathlessness on effort (p less than 0.001). Besides this we have noticed a slight predominance of asthma in boys compared to girls but the difference is not significant.