We studied the correlation between postoperative thyroid histological findings and signal intensities of preoperative magnetic resonance (MR) imaging. The study subjects included 20 cases with thyroid diseases (7 with adenomatous goiter, 2 with follicular adenoma, 6 with papillary carcinoma, 5 with follicular carcinoma). Solid diseases excluding secondary changes (calcification, hemorrhage, necrosis and fibrosis) were investigated by T1 weighted imaging (T1WI) and T2 weighted imaging (T2WI). The results of this study showed that high signal intensities on T1 and T2 indicated preserved follicular structures with a full colloid and sparse atypical cells, in both benign and malignant diseases. Trabecular and microfollicular structures that showed destruction of follicular components and sparse colloid, had a tendency to show low approximately iso signal intensities on T1WI imaging. These results suggest that differentiated grades and the cell proliferative ability of thyroid tumors may be predictable with a combination of T1WI and T2WI.