Background: Onset of puberty in boys usually occurs by 14 years of age. Some boys may exhibit delayed sexual maturation till about 17-18 years of age. However, pubertal onset beyond 18 years of age is exceedingly rare. Materials and Methods: Patients diagnosed as idiopathic hypogonadotropic hypogonadism (IHH) who had onset of puberty (increase in testicular volume >10 ml) while on androgen therapy were studied. These patients were evaluated prospectively. Results: There were nine subjects that were included in the study. The pre-therapy testicular volumes ranged from 3 to 6 ml. Luteinizing hormone (LH) levels increased from 1.2 ± 0.96 to 2.8 ± 1.0 IU/L, follicular stimulating hormone (FSH) levels increased from 1.5 ± 0.79 to 3.5 ± 1.9 IU/L, and testosterone increased from 0.36 ± 0.16 to 3.4 ± 2.1 ng/ml. Three out of nine patients had testosterone levels below 3 ng/ml. Conclusion: Our present study indicates that pubertal development can occur in patients presenting with hypogonadotropic hypogonadism after 18 years of age. However, acquired pubertal status may be subnorma