Background: An American National Intergroup has shown that the risk of cancer recurrence could be reduced by 41% in a group of patients who had undergone a curative resection of colon carcinoma Dukes’ stage C (regional nodal involvement) if they were subsequently treated with levamisole and 5-Fluorouracil (5-FU) in comparison to a group of patients who had undergone surgery only. The mortality rate was reduced by 33%. The study carried out by the Oncological Center of Stuttgart aimed to reproduce these results. Patients and Methods: Having had a curative resection of a colon carcinoma stage TNM III (Dukes’ C), 62 patients were then treated with levamisole and 5-FU for 1 year. Inclusion criteria and levels of dosage of levamisole and 5-FU were the same as those in the study carried out by the National Intergroup. Due to the extremely positive results shown in the National Intergroup study it was considered unethical to include in the Stuttgart study a control group of patients who had undergone surgery only. Results: As severe side effects were observed in the study of the Oncological Center of Stuttgart, the study was already discontinued after a median follow-up time of 15 months (range 1 month to 3.5 years) and the patient data were evaluated. The prognostically relevant characteristics of the levamisole and the 5-FU patient groups in both studies were very nearly identical. This would allow a direct comparison between the two studies. 3.5 years after the beginning of the treatment, 63% of the levamisole and 5-FU patients in the Intergroup study had no cancer recurrence in comparison to 39% of patients in the Stuttgart study. This difference is statistically highly significant. Severe neurotoxic side effects were observed in patients in the Stuttgart study. 2 patients developed multifocal leucencephalopathy, 2 patients fell into coma. Conclusions: As the Stuttgart study could not include a control group of patients who had undergone surgery only, the study is not able to proof the possible ineffectiveness of an adjuvant therapy with levamisole and 5-FU. Considering the study results, however, it would be a sensible and justifiable decision to include a control group in future randomized studies to examine the effectiveness of this adjuvant therapy. We recommend that those patients treated with levamisole and 5-FU should be watched very carefully for neurotoxic side effects