Results: Patients with OP insecticide poisoning showed significant delays in CPT of simple visual reactions (CPTSVR) (p=0.037), CPT of recognition visual reactions (CPTRVR) (p=0.024) and P300 latency (p=0.003) compared to healthy controls. The patients also had a significant impairment in CPTSVR (p=0.017), CPTRVR (p=0.002) and P300 latency (p=0.009) compared to the control group with paracetamol overdose. Comparison of the initial and follow-up findings of the patients revealed that the impairment in CPTSVR (p=0.527) and P300 latency (p=0.867) remained unchanged even six months after poisoning. However, CPTRVR showed a significant improvement (p=0.012). Visual and motor conduction latencies or P300 amplitude were similar between the groups and between the two assessments of the patients with OP poisoning.