Genetic engineering allowed the development of transgenic crops, whose area is planted in 18 countries reaches 67,7 million ha, mainly with plants expressing genes for herbicide tolerance and protection against target insects. Even after rigorous risk assessment, transgenic crops have been a major concern due to potential environmental effects, such as gene flow and impacts on biodiversity. Considering corn and soybean, the risks of horizontal gene flow are remote due to the absence of wild compatible species, whereas such a risk exists for cotton in certain regions of Brazil. The genetic contamination of conventional crops may occur, but this can be prevented by spatial or temporal isolations. Other concern is related to impacts of cultivars expressing insecticide proteins, but the various available studies indicate that the risks of such crops are despicable. The reduction in pesticide use in transgenic croppings may favor biodiversity in comparison to conventional ones, but continued use of glyphosate or Bt crops may favor the development of resistant species and environmental contamination. Such risks however are not exclusive of transgenic cropping. The reviewed studies indicate that transgenic croppings may interfere in the agrisystem, but modifications observed so far, are not different in nature and magnitude from those normally observed in conventional cropping systems. In order to ensure ecosystem biosafety, mitigating practices for eventual risks and monitoring have been recommended for transgenic agrisystems. 