Purpose: Organophosphorus insecticides tend to be regarded as a homogeneous single entity. We aimed to determine whether organophosphate poisoning differs by subgroups in clinical features and severity. Methods: We retrospectively reviewed medical records of all patients with acute organophophorus poisoning from January 1998 to December 2006. We investigated clinical features, Glasgow coma scale (GCS), laboratory findings, QTc intervals, management, and outcomes. Results: A total of 109 patients were included. The dimethoxy group experienced significantly longer times than the diethoxy group for ventilation duration (0.6 day vs. 0.2 day, p=0.006), ICU duration (2.0 day vs. 0.8 day, p=0.037), and total admission duration (2.8 day vs. 0.9 day, p=0.008), except in cases of dichlorvos poisoning. Also, the GCS of the dimethoxy group (except with dichlorvos) was significantly lower than for the diethoxy group (dimethoxy, $11.2{pm}5.2$ vs. diethoxy, $13.8{pm}2.4$, p= 0.021). QTc intervals for the dimethoxy group (except with dichlorvos) tended to be somewhat greater than for the diethoxy group (dimethoxy, $452.9{pm}16.1;msec$ vs. diethoxy, $429.6{pm}40.9;msec$). There were 65 patients with dichlorvos ingestion, and 2 of these patients (3%) died. Conclusion: When compared to the diethoxy group, the dimethoxy group of organophosphates (with the exception of dichlorvos) were associated with poorer prognostic value for indicators such as GCS, QTc interval, requirement for intubation, ICU duration, and total admission duration. Within the dimethoxy group, patients with dichlorvos poisoning had relatively better prognoses than for the other dimethoxy group organophosphates studied.