Morphological investigations were carried out on 184 cases with GCH and related diseases, and the following results were obtained: 1. Pure GCH was observed in 112 cases (60.9%), GCH with ADH in 56 cases (30.4%), and GCH with ATH in 11 cases (6.0%). ECA related with GCH was found in 5 cases (2.7%). 2. It was suggested that GCH can serve as a remote precursor of ECA. Namely, GCH in some cases was found to develop into ECA apparently through the change from ADH to ATH. 3. It was morphologically observed that in GCH, both glandular epithelium and stromal cells were proliferated by being stimulated by estrogen, and such a proliferation was interrupted by an estrogen antagonist, progesterone. On the other hand, in the case of ATH, the growth of stroma was generally decreased and the proliferation of glandular epithelium became predominant. Moreover, the action of progesterone was minimum in ADH and ATH. These findings indicate that precancerous lesions such as ADH and ATH are those capable of developing easily into carcinoma.