Urea is one of the most commonly used nitrogen fertilizers in Romania. The cytogenetic objectives of this experience were the evaluation of the effects of cytotoxicity and genotoxicity induced by the action of urea applied in different concentrations (100, 500, 1000, 5000, 10,000 and 20,000 ppm) for 72 h on the meristematic tissues of Allium cepa L., a species very commonly used in cytotoxicity tests. The statistical analysis of the obtained results indicates that with the increase in urea concentration, mitotic activity is inhibited, while the chromosomal aberration rate in the cells in mitosis as well as the frequency of nuclear abnormalities in the interphase cells increases. From this point of view, the main chromosomal aberrations identified were stickiness, laggards and C-mitosis, while nuclear abnormalities were the appearance of a large number of binuclear and multinucleated cells, some with ghost nuclei. In addition, at concentrations of over 1000 ppm and especially at 10,000 and 20,000 ppm urea the presence of cells with one or more micronuclei (even with nine micronuclei) was signalled, indicating a strong clastogenic potential of urea. The results suggest caution in the use of urea, by applying small concentrations, within the environmental limits, for the protection of the environment, but also of humans and animals. The concentrations we recommend to reduce the risk of pollution are between 100 and 500 ppm urea. However, further investigation is needed to confirm these findings.