The aim of this study was to verify the role of antegrade scrotal sclerotherapy for the treatment of varicoceles in infertile men with severe oligo-astheno-teratozoospermia (OAT). The 59 patients with severe OAT in this study underwent antegrade scrotal sclerotherapy for the treatment of varicoceles. The outcome was assessed in terms of improvement in semen parameters and spontaneous conception rate. Semen parameters and reproductive hormones were evaluated before antegrade sclerotherapy (AS) and 6 months after AS. After an average follow-up time of 34.8±3.2 months, significant improvement was noted in the mean sperm concentration, motility and morphology in 36 patients (61%). Spontaneous pregnancy occurred in nine couples (15%). Six months after treatment, inhibin B levels were significantly higher (P<0.04), whereas follicle-stimulating hormone (FSH) levels were significantly lower (P<0.001) than before treatment. Antegrade internal spermatic vein sclerotherapy can significantly improve seminal parameters and hormonal parameters in men with severe OAT and may even result in spontaneous pregnancy in couples who would otherwise be candidates for intracytoplasmic sperm injection (ICSI).