Aim: The aim of our study was to evaluate pretreatment semen quality in patients with unilateral testicular cancer in comparison to semen parameters of patients suffering from other malignancies. Methods: Semen analysis according to WHO recommendations were performed in 16 patients suffering from unilateral testicular cancer (group 1) and in 21 patients who were diagnosed to have other malignant tumors (group 2: non-Hodgkin's lymphoma: n=7, Hodgkin's disease: n=6, leukemia: n=3, osteosarcoma: n=2, rectal cancer: n=2, thyroid carcinoma: n=1) prior to anti-cancer treatment. Results: Normozoospermia was observed in none of the testicular cancer patients but in five of the other patients (p=0.047). Sperm concentration was significantly decreased in the patients of group 1 compared to those of group 2 (18.7±22.3×106/ml versus 35.6±31.3×106/ml, p=0.03). The percentage of rapid progressive motile spermatozoa was significantly less in testicular cancer patients than in patients suffering from other malignancies (WHO group a: 1.1±2.0% versus 4.7±5.6%, p=0.02). Normal morphological findings of spermatozoa were found in a smaller percentage in group 1 (16.2±6.0% versus 26.1±18.0%, p=0.03). Conclusions: Our investigations revealed that especially testicular cancer has an adverse influence on sperm quality. Hence, we advise careful and sufficient cryopreservation of semen in those patients taking the negative impact of cytotoxic treatments on semen parameters into account.