The cytogenetic effects of dichlorvos on Hordeum vulgare L. seeds were investigated. Seeds of H. vulgare were treated with different concentrations of dichlorvos and applied for increasing concentrations of dichlorvos (0.01, 0.05, 0.1, 0.5 and 1 mg/L) and increased treatment period (10-, 24- and 48-hour) decreased the mitotic index compared with the untreated control. The inhibitory effects of dichlorvos on the mitotic index indicated its genotoxic and mutagenic effects on H. vulgare seeds. It can be concluded that DDVP clearly poses a genotoxic risk. The results of the present study are fundamental results and provide direction for future investigations.