Optimal growth and development in childhood and adolescence is crucial for lifelong health and well-being. Using data from 2,325 population-based studies, with measurements of height and weight from 71 million participants, this paper reports the height and body-mass index (BMI) of adolescents aged 5–19 years based rural and urban residences in 200 countries and territories from 1990 to 2020. In 1990, children and adolescents residing in cities were taller than their rural counterparts in all but a few high-income countries. By 2020, the urban height advantage became smaller in most countries, and in many high-income western countries it reversed into a small urban-based disadvantage. The paper's results show that in much of the world, the growth and developmental advantages of living in cities have diminished in the twenty-first century, whereas in much of sub-Saharan Africa they have amplified.