Consumer concern regarding possible adverse health effects of foods produced using intensive farming methods has led to considerable interest in the health benefits of organically-produced crops and animal products. There appears to be widespread perception amongst consumers that such methods result in foods of higher nutritional quality. The present review concludes that evidence that can support or refute such perception is not available in the scientific literature. A limited number of studies have compared the nutrient compositions of organically- and conventionally-produced crops, with a very small number of studies that have compared animal products (meat, milk and dairy products) produced under the two agricultural systems. Very few compositional differences have been reported, although there are reasonably consistent findings for higher nitrate and lower vitamin C contents of conventionally-produced vegetables, particularly leafy vegetables. Data concerning possible impacts on animal and human health of diets comprising organic or conventional produce are extremely sparse. Data from controlled studies in animal models, particularly within single species, are limited or poorly designed, and findings from these studies provide conflicting conclusions. There are no reports in the literature of controlled intervention studies in human subjects. Comparison of health outcomes in populations that habitually consume organically- or conventionally-produced foods are flawed by the large number of confounding factors that might contribute to any differences reported. If consumer perceptions regarding potential health benefits of organic foods are to be supported, more research of better quality is needed than that which is currently available.