The hypothesis to be tested was that abnormal sperm chromatin structure is related to disturbed spermatogenesis in patients with testicular cancer. After orchiectomy but before further treatment ("pretreatment"), semen samples from 39 patients with testicular cancer were analyzed for sperm concentration by light microscopy and by the sperm chromatin structure assay (SCSA). In 28 patients assessment of sperm concentration was repeated 12-26 months after orchiectomy ("posttreatment"). The pretreatment SCSA results for the patients were compared to those from 18 healthy semen donors and assessed for correlation with the patients' posttreatment sperm concentration. Twenty-three patients displayed an abnormal chromatin structure in their pretreatment sample. For the nine evaluable patients on the surveillance program, the pretreatment SCSA results were not correlated with the posttreatment concentration. The results from 19 evaluable patients undergoing cytotoxic treatment (radiotherapy, 13; chemotherapy, 6) indicate that posttreatment recovery of spermatogenesis (recovery in 4 of 5 patients) is observed more often in patients with a normal pretreatment chromatin structure than in those with abnormal SCSA values before treatment (recovery in 2 of 14 patients; P = 0.02). The results of SCSA display sperm characteristics beyond those of light microscopically assessed sperm concentration. Pretreatment SCSA results might help clinicians to identify those testicular cancer patients with a high risk of long-lasting posttreatment disturbance of spermatogenesis.