Widely varying reports of methods and results have confused evaluation of estrogen as a means of limiting the height of tall girls. This comparative study of 21 treated and 17 untreated girls above the 97th percentile for height indicates a statistically significant probability that exogenous estrogen limits ultimate height, but only by an average of about 4 cm (1.6 in). The optimal starting age appears to be before bone age 13 years. Starting treatment before bone age 111/2 years did not improve results. In offering this treatment, one must weigh the potential ill effects of estrogen administration to young girls against a demonstrated modest decrease in mature height.