This paper, the third in a series, presents data from 28 patients with micropenis categorized as primary hypogonadism (11 subjects), partial androgen insensitivity (1 subject), idiopathic (6 subjects), and etiology undetermined (10 subjects). Among the 11 patients with primary hypogonadism, 8 presented with various degrees of gonadal dysgenesis, 1 was a true hermaphrodite and 2 had the Robinow syndrome. Nine of the 28 patients were raised as females: 5 with primary hypogonadism and 4 with undetermined etiology. Eleven of the 19 patients raised as males received androgen stimulation during prepubertal years and responded with penile growth. However, this growth response was temporary and did not appear to be predictive of eventual adult size of the penis. Generally, the prestimulation size of this group of patients is more predictive of adult penile size. Only 7 of the patients raised as males have attained adult somatic growth. Three out of the three with primary hypogonadism, the subject with partial androgen insensitivity, and one of three with idiopathic micropenis have below-normal adult penile length. These limited data suggest that growth potential of the micropenis may be greater among the patients with an idiopathic state than among those with primary hypogonadism and partial androgen insensitivity.