Phases I and III of the International Study of Asthma and Allergies in Childhood (ISAAC) documented increased asthma symptoms among Nigerian 13-14-year old adolescents. We investigated the trend further using the Global Asthma Network (GAN) surveillance. Using ISAAC methodology, GAN Phase I data on symptoms and risk factors for asthma and asthma management were obtained from February to July 2018. There were 2,897 adolescents from 23 secondary schools. For current wheeze, there was an absolute prevalence fall per decade of -1.4 with -1 standard error (SE) in 16 years from 2002 (ISAAC Phase III) to 2018 (GAN Phase I). This pattern was evident for prevalence of reported asthma ever, severe asthma symptoms and night cough with ≥1 SE. During the 23-year interval between ISAAC Phase I and GAN Phase I, there was a fall (≥1 SE) in the absolute prevalence of reported asthma ever, severe asthma symptoms and night cough, except for severe asthma symptoms (-0.2 SE). Respectively 36% and 43% of symptomatic adolescents purchased and used salbutamol and prednisolone. The prevalence and severity of asthma symptoms remain high among adolescents in Ibadan. This could be mitigated by improved access to affordable and effective asthma treatments.