The present study is dedicated to the human health problems and classification of the most toxic pesticides. Pesticides are a wide range of chemicals with different degree of hazard, from extremely to slightly hazardous. Highly hazardous pesticides may have acute or chronic toxic effects. Their widespread use has caused health problems and fatalities in many parts of the world, often as a result of occupational exposure and accidental or intentional poisonings. Environmental contamination can also result in human exposure through consumption of residues of pesticides in food and, possibly, drinking-water. Recommended classification of pesticides by hazard; carcinogenicity; mutagenicity; reproductive toxicity; listing under the Stockholm Convention on Persistent Organic Pollutants, the Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Pesticides and Industrial Chemicals in International Trade or the Montreal Protocol on Substances that Deplete the Ozone Layer; or evidence of severe or irreversible adverse effects on human health. Keywords: human health problems, toxic impact, pesticides, ecosystem.