Background. Osteosarcoma is a highly malignant bone tumour. After the second relapse, the 12-month postrelapse disease-free survival (PRDFS) rate decreases below 20%. Oral Etoposide is often used in clinical practice after surgery as an “adjuvant” outside any protocol and with only limited evidence of improved survival. Viscum album fermentatum Pini (Viscum) is an extract of mistletoe plants grown on pine trees for subcutaneous (sc) injection with immunomodulatory activity. Methods. Encouraged by preliminary findings, we conducted a study where osteosarcoma patients free from disease after second metastatic relapse were randomly assigned to Viscum sc or Oral Etoposide. Our goal was to compare 12-month PRDFS rates with an equivalent historical control group. Results. Twenty patients have been enrolled, with a median age of 34 years (range 11–65) and a median follow-up time of 38.5 months (3–73). The median PRDSF is currently 4 months (1–47) in the Etoposide and 39 months (2–73) in the Viscum group. Patients getting Viscum reported a higher quality of life due to lower toxicity. Conclusion. Viscum shows promise as adjuvant treatment in prolonging PRDFS after second relapse in osteosarcoma patients. A larger study is required to conclusively determine efficacy and immunomodulatory mechanisms of Viscum therapy in osteosarcoma patients.