The best type, dose and route of estrogen replacement in hypogonadal females has not been fully elucidated and is the subject of this brief review. When feminizing girls with different forms of hypogonadism micronized 17betaE2 should be considered the first choice as it is the most physiological and can be accurately measured in plasma. Most studies of the metabolic effects of the different routes have also used different types of estrogen making comparisons difficult. However, when using the same estradiol compound, 17betaE2 transdermal results in E2, E1 and bioestrogen concentrations closer to normal as compared to oral and achieves greater suppression of LH/FSH but similar IGF-I and lipid concentrations. Whether this translates into better body composition and metabolic outcomes in girls with hypogonadism is being actively investigated and data will soon be available.