Severe forms of male-factor infertility are associated with an increased risk of testicular cancer and scrotal ultrasonography is widely used for diagnosis. In this study, 2172 male members of infertile couples referred to our Reproductive Medicine Unit were submitted to scrotal ultrasonography and 835 selected patients had been followed during a 2-year period. Eight out of nine neoplastic nodules found at the initial examination were unpalpable and discovered by ultrasonography. Ten tumoral lesions were found in 370 testicular biopsies performed for diagnostic purposes or to extract spermatozoa; and eight additional neoplastic lesions were discovered during the 2-year follow-up of 835 patients. The cumulative rate of neoplastic disease was 3.2%. Thirteen cases (1.5%) were malignant (12 germ cell tumours and one non-Hodgkin lymphoma of testicular origin); the remaining 14 were benign forms (Leydig cell tumours and hyperplasias, Sertoli cell nodules, adenomatoid tumours). Testicular volume (cut-off: 12ml) resulted weakly correlated with germ cell cancer (p=n.s., odds ratio 2.01) while low total sperm count (<40x10(6)) (p=0.002, odds ratio 8.4), previous cryptorchidism (p=0.04, odds ratio 7.5) and hypergonadotrophic hypogonadism (p=0.04, odds ratio 7.9) were associated with an increased risk. But a stronger correlation with germ cell cancer was found in the patients with some utrasonographic anomalies, i.e. testicular microlithiasis (p=0.0015, odds ratio 37.1) or larger calcifications not fitting the description of testicular microlithiasis (p<0.0001, odds ratio 69.5). Our findings indicate that scrotum ultrasonography should always be advised in subfertile men with <40x10(6) spermatozoa/ejaculate or hypergonadotrophic hypogonadism or previous cryptorchidism, and that particular care should be taken in the presence of testicular microlithiasis or testicular calcifications. These men should be aware of the existence of higher risk of testicular cancer and trained in testicular self-examination.