Delayed puberty can be defined as the absence of any signs of puberty in subjects that have attained an age at the upper limit (+2DS) for the onset of puberty, that means 13 years in girls and 14 years in boys. The causes of delayed puberty can be classified into three groups, functional temporary impairment in gonadotropin and sex steroid secretion (most frequently constitutional delay of puberty), hypothalamo-pituitary failure with deficiency in gonadotropin secretion, primary gonadal failure with increased gonadotropin levels. The Authors discuss about etiology, diagnostic testing and therapeutic approach in these conditions. The majority of children with delayed puberty are males that have only a constitutional delay of growth and puberty. It is difficult, in teenage years, to distinguish this common and benign condition from true gonadotropin deficiency, in spite of the variety of endocrine tests developed for this purpose. Individuals with constitutional delayed puberty with a bone age greater than 11.5 years, show after triptorelin stimulation an increase in LH capable of distinguishing them from patients with gonadotropin deficiency. In our opinion this could be an important screening test to exclude gonadotropin deficiency in boys with delayed puberty.