A 35-year-old man and his partner were referred for intracytoplasmic sperm injection treatment (ICSI) because of secondary infertility due to severe oligoasthenoteratospermia. Three years earlier he had presented elsewhere with left unilateral gynaecomastia. A hypertrophic mammary gland had been excised one year later. Histopathological investigation showed benign hypertrophy. One year later he developed gynaecomastia on the other side. Physical examination and incomplete hormonal screening showed no abnormalities. The couple were referred to our tertiary clinic for ICSI treatment. The patient still had unilateral gynaecomastia. Hormonal screening showed not only severe oligoasthenoteratospermia, but also an elevated serum oestrogen level. Scrotal ultrasound revealed a 17 mm mass in his right testicle. Subsequently unilateral orchidectomy was performed. Histology showed a benign Leydig cell tumour for which no further therapy was required. Four months after surgery the gynaecomastia diminished, oestrogen levels became normal and improvement in semen parameters followed. Patients with severe male infertility or gynaecomastia are at a higher risk of developing a testicular neoplasm. Besides history taking, physical examination of breasts and testicles, hormonal screening and scrotal sonography should be performed as some testicular neoplasms are not apparent on palpation.