Geographic differences have been reported to affect the morphological and molecular features of papillary thyroid carcinomas (PTCs). The area around Chernobyl is well-known to be iodine-deficient in contrast to Japan, an iodine-rich country. We reviewed histological differences in adult PTC between Ukraine and Japan. In total, 112 PTCs from age- and sex-matched adults (Ukraine 56, Japan 56) were evaluated histologically for several factors including tumor size, capsulation, tumor components (papillary, follicular, solid, trabecular), lymph node metastasis, extrathyroid invasion, lymphocytic infiltration, oxyphilic metaplasia, and MIB-1 index. We demonstrated that tumors were smaller (1.56 vs. 2.13 cm, p<0.05) and more solid and that lymph node metastasis was less frequent (14.3% vs. 48.2%, p<0.001) in Ukrainian cases. PTC subtype distribution was significantly different between the two groups. Solid variant (8.9% vs. 1.8%) and mixed subtypes with solid components were more frequent in Ukrainian patients. In contrast, classical papillary carcinomas were more frequent in Japanese cases (10.7% vs. 50.0%, p<0.001). Marked oxyphilic metaplasia was more common in Ukrainian cases (33.9 % vs. 8.9 %, p<0.001). MIB-1 index was significantly higher in Ukrainian cases (2.9% vs. 1.8%, p<0.001). However, the frequencies of tumor capsule formation and background lymphoid follicle formation around the tumor were similar between groups. Morphological differences in adult PTCs were similar to those in pediatric PTCs as reported previously, suggesting that morphogenesis of PTC is influenced by environmental factors, especially dietary iodine, as well as genetic factors.