Organophosphates (OPs) and Pyrethroids (PYRs) are widely used pesticides in both agricultural and non-agricultural environments. In agricultural work settings, typically more than one pesticide is used in combination, or sequentially, to kill pests. There is currently a gap in research that looks at how exposures to multiple pesticides can impact human health – particularly among adolescents who work in these environments. The goal of this dissertation research was to examine the use of OP (chlorpyrifos, and profenofos) and PYR (λ-Cyhalothrin, α-Cypermethrin) pesticides across an application season and how exposure is associated with symptoms and cholinesterase enzyme activity, and to examine the impact of a sequential exposure to multiple OPs, and exposure to both OPs and PYRs. Urine and blood samples, questionnaire data, and a medical exam were collected over a 10-month period from adolescent pesticide applicators in Egypt. Overall, applicators had higher exposure than non-applicators to all four pesticides. The non-applicators were also exposed and had levels 4 times higher in urine metabolite levels than the general population in the U.S. In addition, these exposures caused increased symptoms and severity of symptoms among both applicators and non-applicators. In conclusion, adolescent agriculture workers in the Egyptian cotton fields are exposed to multiple pesticides and are susceptible to the impact of those exposures on their health.