Risk assessment studies of transgenic crops have recently brought evidence of a low spontaneous hybridization frequency of Brassica napus with Raphanus raphanistrum. The fate of the first generation hybrids is crucial to determine the initial rate of spread of transgenes. This work aims to compare the fitness components of parents and F1 hybrids at the first step of the life cycle. The ability to emerge, establish seedling, cover the soil and develop adult plant was examined in controlled and field conditions, alone or in competition. The F1 hybrids showed a lower seedling emergence, a significant delay of emergence, and a lower survival than for both parents. Rosette diameter and dry matter of hybrid plants were very reduced compared with those of both parents, especially when they grew in the field and under competition conditions. The relevance of these results to gene flow and possible impact to agriculture and environment is discussed.