To evaluate gonadal function in male adolescents and young men with juvenile onset systemic lupus erythematosus (SLE).Four young men with SLE underwent clinical and laboratory evaluation, testicular ultrasound, follicle stimulating hormone, luteinizing hormone, prolactin, testosterone, and anti-sperm antibody determination. The semen analyses were performed according to the WHO guidelines and Kruger strict criteria. All patients were asked to provide 3 semen samples over a period of 2 months. A new sample was collected 6 months later.The median disease duration was 6.6 years. The median age at initial ejaculation was 13.5 years. All 4 patients had severe disease with renal involvement (WHO class IV or V). The SLICC/ACR damage index at the time of study entry ranged between 0 and 3. The patients' Tanner stage was P5G5; all reported normal erection and libido. Gonadal evaluation by thorough examination of the genitalia and ultrasound was normal. Anti-sperm antibodies were negative in all patients. Only one patient showed high FSH and LH levels. The initial and final semen evaluations of the 4 patients were abnormal (azoospermia, oligoastenoteratospermia, or teratospermia). One patient was receiving azathioprine and 2 were receiving cyclophosphamide at the time of study entry.Although these patients had normal sexual activity and normal external genitalia, their fertility was decreased based on the sperm abnormalities. Serial semen analyses in larger study populations will be necessary to clarify the degree and duration of sperm abnormalities in male patients with SLE in general.