The idea that UV radiation causes cataract has superficial biological plausibility based upon studies of UV-B on lens components, whole lenses and experimental animals. However, epidemiological studies on man, particularly geographical studies, are highly confounded by socioeconomic factors and yield little information. Population-based exposure-cataract studies are preferable since UV incidence versus UV exposure can be weighted with respect to risk and protective factors. However, the cataractogenic potency of UV seems to be low and certainly lower than the cataractogenic potency of factors such as repeated diarrhoea so that it is doubtful whether a clear answer to the question 'Does UV cause cataract' will ever be provided.