Pubertal gynecomastia is common, and may affect up to 70% adolescents boys. Its course is spontaneously benign with resolution occurring by age 18 years. Although the exact physio-pathological mechanism remains unknown, it is thought to result from hormonal imbalance between estrogens and testosterone at puberty. Association with Leydig cell tumour is more common in adults, so that scrotal ultrasound is part of routine work up. A 15-years-old boy with Leydig cell tumour revealed by bilateral gynecomastia is reported. Diagnosing this condition requires high level of suspicion, we suggest that clinicians always do a testicular examination on adolescents especially if they have gynecomastia, scrotal ultrasound may be performed in boys aged > or =14 years with gynecomastia that measures > or =4 cm, should there be any doubt.