Absence of any sign of gonadal development (i.e. increase in size of the testes or presence of breast budding) before the age of 13 years in girls and 14 years in boys represents the condition of delayed sexual maturation. After this age, the patient should be thoroughly clinically examined and a basic biological work-up should be performed. Pathological conditions such as hypergonadotropic hypogonadism with a bone age usually greater than 13 years can be easily diagnosed. Hypogonadotropic hypogonadism is more difficult to differentiate from delayed adolescence of good prognosis. Means of diagnosis as well as therapy are discussed. In addition, micropenis and primary amenorrhea are frequent clinical observations.