Despite a warm sunny climate, rickets is extremely common in children living in an isolated mountainous area of North Yemen. In a small township the overall prevalence amongst children under five years attending for vaccination was 27%. The condition was most common at the end of the first year and had disappeared by the fifth year. Marasmus was commonly associated with rickets. Children from the rural villages outside the township had significantly lower rates of rickets. Several factors may contribute to the very high rates of rickets in rural Yemen. However, lack of exposure to sunlight as a consequence of particular cultural practices is likely to be the most important. The major social and behavioural factors which restrict the young child access to sunlight are outlined, and possible remedies discussed.