This review is focused on the diagnosis, clinical and general therapeutic approach of constitutional growth and puberty delay and hypogonadotrophic hypogonadism in males, two entities that are difficult to distinguish. Clinical history and physical examination must be carefully performed. Delayed puberty is due to constitutional growth and puberty delay in the vast majority of children. These must be distinguished from a small fraction of boys with hypogonadism, a pathological condition. A number of laboratory test allow the prediction of puberty onset and progression. Nevertheless, the advent of highly sensitive immunoassay and radiometric immunoassay systems for LH, FSH and testosterone has not entirely solved the problems, since their values may overlap between normal and pathological conditions.