Purpose: Although glyphosate-surfactant herbicide intoxication is relatively mild toxic in humans, we encountered an atypical clinical presentation. We performed this study to understand the atypical clinical course and factors associated with severe intoxication after glyphosate ingestion. Methods: We conducted a retrospective study of 61 patients (male 43, mean age $54{pm}18.8$ years) who were presented with glyphosate ingestion between March 1997 and March 2011. The severe intoxication group was defined as patients with systolic blood pressure less than 90 mmHg, respiratory distress needing intubation, or altered mental state. Results: Of the 61 patients, 22 patients (36.1%) had a severe clinical course, 1 patient (1.6%) had died and 1 patient (1.6%) had moribund discharge. The most common symptoms were nausea with or without vomiting which occurred in 30 patients (49.2%). Twenty-seven patients had metabolic acidosis that was the second most common medical complication. Advanced age, pH, base excess, $HCO_3$, Sat, creatinine, X-ray abnormalities and ECG abnormalities were significant factors. Hemoglobin, platelet, $pO_2$, $pCO_2$, BUN, sodium, potassium and AST levels were not different comparing the laboratory characteristics between the severe and mild intoxication groups. Conclusion: The results of this study showed that severe intoxication occurred in 22 patients (36.1%) after glyphosate intoxication. Advanced age, pH, base excess, $HCO_3$, Sat, creatinine, X-ray abnormality and ECG abnormalities were significant predictive factors for severe intoxication in patients with glyphosate surfactant herbicide poisoning.