The aim of the present study was to determine if the differential diagnosis between lobular endocervical glandular hyperplasia (LEGH) and minimal deviation adenocarcinoma (MDA), or 'adenoma malignum', is reproducible when clear criteria for these two lesions are given. A total of 44 proliferative endocervical glandular lesions were collected, for which differential diagnosis from MDA was considered to be necessary. Seven observers independently classified these 44 lesions into LEGH, LEGH with adenocarcinoma in situ (AIS), MDA, or common cervical adenocarcinoma, according to the following criteria: LEGH was non-invasive proliferation of endocervical glandular cells without any obvious adenocarcinoma component. MDA was very well-differentiated endocervical-type mucinous adenocarcinoma composed mostly of LEGH-looking glands but containing the component of obviously invasive adenocarcinoma. LEGH with AIS was defined as continuous coexistence of LEGH and AIS. Among these four diagnostic categories, the interobserver agreement level was substantial (kappa = 0.618). The level increased to almost perfect (kappa = 0.928) between the group of non-invasive lesions consisting of LEGH and LEGH with AIS and the other group of invasive lesions comprising MDA and common adenocarcinoma. When the modal diagnosis was adopted as the final diagnosis for individual lesions, the 5 year survival rate of patients after surgery was 100% for the non-invasive lesions but only 54% for the invasive lesions (P < 0.01). It is clearly shown that reproducible differential diagnosis is possible between LEGH, LEGH with AIS, and MDA and that such a differentiation is clinically meaningful.