We analyzed the incidence of structural and numerical chromosomal aberrations (CAs) in workers of a plantation of flowers located in Quito, Ecuador, in South America. This study included 41 individuals occupationally exposed to 27 pesticides, some of which are restricted in many countries and are classified as extremely toxic by the World Health Organization: among these are aldicarb and fenamiphos. The same number of individuals of the same age, sex. and geographic area were selected as controls. Workers exposed to these pesticides showed an icreased frequency of CA compared with control group (20.59% vs. 2.73%; p < 0.001). We conclude that screening for CA is an adequate biomarker for evaluating and detecting genotoxicity resulting from exposure to pesticides. Levels of erythrocyte acetylcholinesterase were also determined as a complementary metabolic study. Levels of the optimal (> 28 U/mL blood) were found in 88% of exposed individuals; this clearly shows the effect of organophosphate pesticides. When comparing the levels of acetylcholinesterase and structural CA frequencies, there was a negative linear correlation (r = 0.416; p < 0.01). We conclude that by using both analyses it may be possible to estimate damage produced by exposure to organophosphate pesticides.