Surgical removal of bulky metastases of non-seminomatous germ-cell testicular cancer has been advocated as an adjuvant to chemotherapy in patients whose disease probably is too extensive to be cured by chemotherapy or surgery alone. However, in 8 of our patients, cytoreductive surgery was followed by a sudden and dramatic exacerbation of the disease. In some cases, a marked rise in the serum levels of alpha-fetoprotein and human chorionic gonadotropin was the only evidence. The cause and prevalence of such exacerbations are unknown. Cytoreductive surgery in patients with advanced testicular tumor is accepted treatment and should be advocated, but it appears that in some cases such surgery may adversely alter the course of the malignancy. This must be considered in planning treatment for patients with advanced disease.